pgsql: Reduce the maximum value of vacuum_cost_delay and

Log Message:
-----------
Reduce the maximum value of vacuum_cost_delay and autovacuum_vacuum_cost_delay
to 100ms (from 1000).  This still seems to be comfortably larger than the
useful range of the parameter, and it should help discourage people from
picking uselessly large values.  Tweak the documentation to recommend small
values, too.  Per discussion of a couple weeks ago.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.210 -> r1.211)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.210&r2=1.211)
    pgsql/src/backend/access/common:
        reloptions.c (r1.21 -> r1.22)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/reloptions.c?r1=1.21&r2=1.22)
    pgsql/src/backend/utils/misc:
        guc.c (r1.495 -> r1.496)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.495&r2=1.496)
        postgresql.conf.sample (r1.253 -> r1.254)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.253&r2=1.254)
    pgsql/src/test/regress/expected:
        guc.out (r1.6 -> r1.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/guc.out?r1=1.6&r2=1.7)
    pgsql/src/test/regress/sql:
        guc.sql (r1.6 -> r1.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/guc.sql?r1=1.6&r2=1.7)