Added non-linear posix tree based ldap support via basic ldap search

Added non-linear posix tree based ldap support via basic ldap search.


If your ldap tree is non liner like:
   uid=admin,ou=admins,ou=people,dc=com
   uid=user1,ou=group1,ou=people,dc=com
   uid=user2,ou=group1,ou=people,dc=com
   uid=user3,ou=group2,ou=people,dc=com
   uid=user4,ou=group2,ou=people,dc=com

You can not use basic bind for authentication unless you use full or partial dn's instead of user names. If this is the case, you may use a user account that's capable of searching your user tree and retrieve the full dn of a user. 

With this patch I've added this operation via basic php-ldap extension calls. But for this to work you need to use these settings (using this sample tree):

ldap_mode = posix-search
ldap_bind_dn = uid=admin,ou=admins,ou=people,dc=com
ldap_bind_passwd = (admin users bind password)
ldap_search_base = ou=people,dc=com