Grant problem and how to prevent users to execute OS commands?

Hello List,
First time here also beginner to Postgres.So please forgive me for any mistakes.
I'm pretty sure i have same problem.=> http://archives.postgresql.org/pgsql-admin/2012-03/msg00105.php
(After searching it i found it)
However it is not solution for me.:( *I'm pretty sure i'm doing something in wrong manner*.
After issusing that revoke from public my postgres user still able to connect to any database.
More over
  when executing \l user is able to see complete database names.

So i have 2 questions:
1 ) How i can grant my user(s) to connect only to *granted* database not *any*
2 ) Users still able to execute OS (operation system) commands on system.
This is a big security risk.How i can prevent it too.

Any recommendations,manuals,helps,hints,RTFM :P are welcome;)

Thanks in advance.

OS: Windows XP sp2 32 bit+Cygwin.
And here is what i'm doing (For *picture* my situation)






===================BEGIN============================
$ psql -h localhost -U postgres -p 5432
Password for user postgres:
psql (9.1.4)
WARNING: Console code page (866) differs from Windows code page (1251)
          8-bit characters might not work correctly. See psql reference
          page "Notes for Windows users" for details.
Type "help" for help.

postgres=# \dt
No relations found.
postgres=# \l
                                            List of databases
      Name     |  Owner   | Encoding |       Collate       |        Ctype        |   Access privileges
--------------+----------+----------+---------------------+---------------------+-----------------------
  mytestdb     | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 |
  onlypostgres | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 |
  postgres     | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 |
  template0    | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 | =c/postgres          +
               |          |          |                     |                     | postgres=CTc/postgres
  template1    | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 | =c/postgres          +
               |          |          |                     |                     | postgres=CTc/postgres
(5 rows)


postgres=# \dg
                              List of roles
  Role name |                   Attributes                   | Member of
-----------+------------------------------------------------+-----------
  postgres  | Superuser, Create role, Create DB, Replication | {}


postgres=# select version() \g
                            version
-------------------------------------------------------------
  PostgreSQL 9.1.4, compiled by Visual C++ build 1500, 32-bit
(1 row)

postgres=# create user testusr with password 'testpwd' \g
CREATE ROLE
postgres=# \dg
                              List of roles
  Role name |                   Attributes                   | Member of
-----------+------------------------------------------------+-----------
  postgres  | Superuser, Create role, Create DB, Replication | {}
  testusr   |                                                | {}


postgres=# create database testdb \g
CREATE DATABASE
postgres=# \timing
Timing is on.
postgres=# \c testdb
WARNING: Console code page (866) differs from Windows code page (1251)
          8-bit characters might not work correctly. See psql reference
          page "Notes for Windows users" for details.
You are now connected to database "testdb" as user "postgres".
testdb=# \d
No relations found.
testdb=# create table test_tbl(id serial,somecol text) \g
NOTICE:  CREATE TABLE will create implicit sequence "test_tbl_id_seq" for serial column "test_tbl.id"
CREATE TABLE
Time: 102,137 ms
testdb=# \c
WARNING: Console code page (866) differs from Windows code page (1251)
          8-bit characters might not work correctly. See psql reference
          page "Notes for Windows users" for details.
You are now connected to database "testdb" as user "postgres".
testdb=# \d
                List of relations
  Schema |      Name       |   Type   |  Owner
--------+-----------------+----------+----------
  public | test_tbl        | table    | postgres
  public | test_tbl_id_seq | sequence | postgres
(2 rows)


testdb=# grant all on database testdb to testusr \g
GRANT
Time: 3,638 ms
testdb=# \dg
                              List of roles
  Role name |                   Attributes                   | Member of
-----------+------------------------------------------------+-----------
  postgres  | Superuser, Create role, Create DB, Replication | {}
  testusr   |                                                | {}


testdb=# \dp
                                  Access privileges
  Schema |      Name       |   Type   | Access privileges | Column access privileges
--------+-----------------+----------+-------------------+--------------------------
  public | test_tbl        | table    |                   |
  public | test_tbl_id_seq | sequence |                   |
(2 rows)


testdb=# \q

user@SHELL ~
$ psql -h localhost -U testusr -p 5432 -d testdb
Password for user testusr:
psql (9.1.4)
WARNING: Console code page (866) differs from Windows code page (1251)
          8-bit characters might not work correctly. See psql reference
          page "Notes for Windows users" for details.
Type "help" for help.

testdb=> \l
                                            List of databases
      Name     |  Owner   | Encoding |       Collate       |        Ctype        |   Access privileges
--------------+----------+----------+---------------------+---------------------+-----------------------
  mytestdb     | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 |
  onlypostgres | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 |
  postgres     | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 |
  template0    | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 | =c/postgres          +
               |          |          |                     |                     | postgres=CTc/postgres
  template1    | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 | =c/postgres          +
               |          |          |                     |                     | postgres=CTc/postgres
  testdb       | postgres | UTF8     | Russian_Russia.1251 | Russian_Russia.1251 | =Tc/postgres         +
               |          |          |                     |                     | postgres=CTc/postgres+
               |          |          |                     |                     | testusr=CTc/postgres
(6 rows)


testdb=> \c onlypostgres
WARNING: Console code page (866) differs from Windows code page (1251)
          8-bit characters might not work correctly. See psql reference
          page "Notes for Windows users" for details.
You are now connected to database "onlypostgres" as user "testusr".
onlypostgres=> \d
              List of relations
  Schema |    Name    |   Type   |  Owner
--------+------------+----------+----------
  public | wtf        | table    | postgres
  public | wtf_id_seq | sequence | postgres
(2 rows)


onlypostgres=> # WHY THIS testusr is able to connect to all databases? In fact it is not granted for this.:(
onlypostgres(> \r
Query buffer reset (cleared).
onlypostgres=>

onlypostgres=> \! ping google.com

Обмен пакетами с google.com [173.194.71.113] по 32 байт:

Ответ от 173.194.71.113: число байт=32 время=432мс TTL=44
Ответ от 173.194.71.113: число байт=32 время=437мс TTL=44
Ответ от 173.194.71.113: число байт=32 время=437мс TTL=44
Ответ от 173.194.71.113: число байт=32 время=497мс TTL=44

Статистика Ping для 173.194.71.113:
     Пакетов: отправлено = 4, получено = 4, потеряно = 0 (0% потерь),
Приблизительное время приема-передачи в мс:
     Минимальное = 432мсек, Максимальное = 497 мсек, Среднее = 450 мсек
onlypostgres=> # I have also second problem.How i can prevent users to execute OS command?(I don't want users will be
ableto execute OS c 
ommands
onlypostgres'> \r
onlypostgres'># THANKS.
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