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)