Made em_fg_gatekeeper_delete less noisy for unmodified fields.
Added revert for field_groups.
Fixed group status.

Sanity fix of gatekeeper_delete: don't try to revert when there's no instances.
Fixed more stupidity causing revert to not work.
Fixed stupidity in gatekeeper_delete..
Removed odd code.

Fixed reverting of field_gatekeeper.
Handling of missing export hook in diff command.