restore search detail selector hack in LdapGroupPersistence, fix deleteGroup so it properly clears members

small tweaks and fixes to get integration tests to pass; removed support for querying for other user memberships in GMSClient API

ac2 - Changed thread safety in LdapPersistence.  Removed the returning of groups from the add and modify group persistence APIs

added GroupDetailSelector so GroupPersistence implementation can configure whether group details should be returned from searches

implemented public-attribute-only get option so caller doesn't need permission to get a member group

add check timeout codes and throw TransientException; re-implement checkgroupExists as a filtered search instead of using getGroupNames

made modest retry for all transient failures the default in ca.nrc.cadc.net; improved some error handling for ldap timeout