Hello

This is improvement to map custom user fields in auth LDAP.
It is more compact and strongly refactored Olav Jordan's
patch from MDL-10908.

It should works with other auth plugins (not tested) after adding
to it's countructor following row like in 'auth/ldap/auth.php' one:

$this->addCustomToUserFields();

I also do not test it's impact on auth_ldap_sync_users.php,
because I use something different to sync users.