Adding usernames to pg_hba.conf

This patch completes the following TODO item:

* Allow usernames to be specified directly in pg_hba.conf (Bruce)

Currently, we allow usernames in secondary password files, but this is a
very confusing feature. This patch:

o removes secondary password file support
o adds a user name column just after the database column
o allows a comma separated list of usernames or databases
o allows another file to contain a list of username/databases
by preceding the pg_hba.conf entry with '@'
o allow single or double-quoting of user/database names

See the documentation changes and new pg_hba.conf diffs for samples.

Is the '@' sign a good way to identify a file name? Is putting the
username column just after the database column the right place for it?

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026