change ldap group lookup when using memberUid to match using name

according to rfc2307 which says the memberUid is a name (not a uid
strangely enough)

just going by
http://manpages.ubuntu.com/manpages/natty/man5/sssd-ldap.5.html
ldap_schema description and my broken install on ubuntu...

I can't say what ldif I used except it was standard (I didn't write it)
and ldapscripts and phpmyadmin all seem to want the field to be a name.