pgsql: Add a log_file_mode GUC that allows control of the file

Log Message:
-----------
Add a log_file_mode GUC that allows control of the file permissions set on
log files created by the syslogger process.

In passing, make unix_file_permissions display its value in octal, same
as log_file_mode now does.

Martin Pihlak

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.295 -> r1.296)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.295&r2=1.296)
    pgsql/src/backend/postmaster:
        syslogger.c (r1.58 -> r1.59)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/syslogger.c?r1=1.58&r2=1.59)
    pgsql/src/backend/utils/misc:
        guc.c (r1.561 -> r1.562)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.561&r2=1.562)
        postgresql.conf.sample (r1.290 -> r1.291)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.290&r2=1.291)
    pgsql/src/include/postmaster:
        syslogger.h (r1.16 -> r1.17)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/postmaster/syslogger.h?r1=1.16&r2=1.17)