pgsql: * make pg_hba authoption be a set of 0 or more name=value pairs *

Log Message:
-----------
* make pg_hba authoption be a set of 0 or more name=value pairs
* make LDAP use this instead of the hacky previous method to specify
the DN to bind as
* make all auth options behave the same when they are not compiled
into the server
* rename "ident maps" to "user name maps", and support them for all
auth methods that provide an external username

This makes a backwards incompatible change in the format of pg_hba.conf
for the ident, PAM and LDAP authentication methods.

Modified Files:
--------------
pgsql/doc/src/sgml:
client-auth.sgml (r1.108 -> r1.109)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml?r1=1.108&r2=1.109)
pgsql/src/backend/libpq:
auth.c (r1.168 -> r1.169)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c?r1=1.168&r2=1.169)
hba.c (r1.168 -> r1.169)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c?r1=1.168&r2=1.169)
pg_hba.conf.sample (r1.64 -> r1.65)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pg_hba.conf.sample?r1=1.64&r2=1.65)
pg_ident.conf.sample (r1.8 -> r1.9)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pg_ident.conf.sample?r1=1.8&r2=1.9)
pgsql/src/include/libpq:
hba.h (r1.49 -> r1.50)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/hba.h?r1=1.49&r2=1.50)