This patch adds a common "base filter" for creating authproc filters
that access a LDAP directory, and it adds a filter
(ldap:AttributeAddUsersGroups) for adding group information.

Thanks to Ryan Panning for implementing this!

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@2986 44740490-163a-0410-bde0-09ae8108e29a