BUG #11233: Wishlist: specify config file directory independently

The following bug has been logged on the website:

Bug reference:      11233
Logged by:          Ed Avis
Email address:      eda@waniasset.com
PostgreSQL version: 9.3.5
Operating system:   Linux (Fedora 20)
Description:

If you want to keep the configuration files somewhere other than their
default location, you must pass the -D option to postgres to change the
DATADIR, which is really the config file directory, and then change
pg_hba.conf to point the data directory back to its original location.

This is a bit more awkward than it needs to be.  I suggest disentangling the
two variables 'data directory' and 'config file directory'.  Then a new -C
CONFIGDIR option to postgres would change the location of the config files
without changing DATADIR.  This would mean you could move the config files
to a new place, pass it with -C, and you're done.