keep "add principal" input be focused when it's been clicked

when clicking the "add principal" input (e.g. #AddPrincipalForRights-group),
anchor will be synced to #acl-AddPrincipal, but the input focus will be lost
too(at least on firefox).
Merge branch '4.2/admin-rights-add-principal-input-focus' into 4.2-trunk