[WIP] Patch : Change pg_ident.conf parsing to be the same as pg_hba.conf

Attached is a Patch to change the parsing of pg_ident.conf to make it
similar to pg_hba.conf.
This is based on Todo Item:
http://archives.postgresql.org/pgsql-hackers/2011-06/msg02204.php

Purpose - This will allow to catch syntax errors in pg_ident at the startup
or reload time.


Changes are described as follows:
a. Make the load_ident() functionality same as load_hba, such that it
cleans the previous context, after successful parsing.
b. Change the load_ident(), so that parsing can be done during load
time and the parsed lines are saved.
c. Change the functionality of parse_ident_usermap() so that parsing is
not done during authentication.
d. If load_ident() fails for parsing, it returns false and error is
issued.
This point I am not sure, as for pg_hba failure it issues FATAL at
startup. Currently I have kept error handling for load of pg_ident same as
pg_hba

I have done the basic testing and test is still in progress.

Suggestions?


With Regards,
Amit Kapila.