streamlining auth backends :!:

This patch is a start to make all the auth backend mor alike in
configuration and to update all backend to the new OO method.

This patch changed some config placeholders and thus may break
existing configs! Here is a list of the new place holders used
in MySQL and LDAP:

%{user}   - the login name
%{group}  - a group name
%{pass}   - the password (cleartext or crypted)
%{dgroup} - the default group
%{guid}   - a group id
%{uid}    - a user id
%{name}   - full name of a user
%{email}  - email of a user
%{dn}     - DN for a user (LDAP only)

The LDAP backend was enhanced a little bit. The default group
now is always added to the list of returned groups. A different
Server Port can be configured.

More changes will follow.

darcs-hash:20060121181149-7ad00-79de68aa7f87aef87dcff9dd7afd50adda859289.gz