Thread: pgsql: Update documentation about postgresqlconf to mention default

Log Message:
-----------
Update documentation about postgresqlconf to mention default units that
match the postgresql.conf file.  Also add units to descriptions that
lacked them.  Wording improvements.  Mention pg_settings.unit as the way
to find the default units for setting.

Backpatch to 8.2.X.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.103 -> r1.104)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.103&r2=1.104)