pgsql: Add hba parameter include_realm to krb5, gss and sspi

Log Message:
-----------
Add hba parameter include_realm to krb5, gss and sspi authentication, used
to pass the full username(at)realm string to the authentication instead of
just the username. This makes it possible to use pg_ident.conf to authenticate
users from multiple realms as different database users.

Modified Files:
--------------
pgsql/doc/src/sgml:
client-auth.sgml (r1.116 -> r1.117)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml?r1=1.116&r2=1.117)
pgsql/src/backend/libpq:
auth.c (r1.176 -> r1.177)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c?r1=1.176&r2=1.177)
hba.c (r1.179 -> r1.180)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c?r1=1.179&r2=1.180)
pgsql/src/include/libpq:
hba.h (r1.54 -> r1.55)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/hba.h?r1=1.54&r2=1.55)