[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.