Start of an LDAP authentication setup for poweradmin

at the moment it totally ignores internal users; adding and removing users in poweradmin when $auth_mode is set to 'ldap' does still add users; but these sql users can not be used to log in (while $auth_mode is set to ldap). 

LDAP users get an user ID of '1', which matches the default 'admin' user, and are being treated as ueberusers.