Re: Thoughts on the location of configuration files, how about this:

Noting Peter's thought on the matter and merging some of the things I think are
important, I wrote this down as a sort of way of flushing out the precise
meaning of the configuration options:

Command line options:
-C filepath_name
If filepath_name is a file, it is treated as a configuration file, no other
information is assumed. If filepath_file is a directory, it is used to replace
the default "sysconfdir" obtained from configure. 

-D datadir
the -D option overrides any default setting, and any setting in
postgresql.conf.

Other options
All other options override the defaults set by either the "configure" operation
or the active postgresql.conf file.

postgresql.conf
By default it will live in sysconfdir as configured by "configure." 
If it is not found in the "sysconfdir," $PGDATA will be searched.
Using the "-C" option forces the file's explicit location. If "-C" is
specified, postgresql.conf (or filename) must exist as specified in accordance
with the documented "-C" behavior.
It may contain a setting "hbaconfig" which will override the default location.
It may contain a setting "identconfig" which will override the default
location.
It may contain a setting "datadir" which will override the default location.

pg_hba.conf
By default it will live in sysconfdir as configured by "configure."
Its location can be changed by "hbaconfig" in postgresql.conf.
If not configured in postgresql.conf and not found within "sysconfdir," $PGDATA
will be searched. If explicitly configured in the postgresql.conf file, it must
exist as specified.

pg_ident.conf
By default it will live in sysconfdir as configured by "configure."
Its location can be changed by "identconfig" in postgresql.conf.
If not configured in postgresql.conf and not found within "sysconfdir," $PGDATA
will be searched. If explicitly configured in the postgresql.conf file, it must
exist as specified.

PGDATA
The data directory will be found in the directory configured by GNU "configure"
If the environment variable PGDATA is specified, it overrides the configured
default.
If the postgresql.conf file contains "datadir" it overrides the previous other
two.
If the command line "-D" option is used, it overrides the previous three.


Note:
I think the data directory should be explicitly configured by either the
posgresql.conf file, environment variable (PGDATA), or through the command line
option, but using the "configure" statedir isn't anything anyone would object
too.


What do you all think? 
Is anything ambiguous?
Is anything wrong?
Can we all agree this is how it should be?