Blender Git Loki

Fix missing undo pushes in outliner's new datablock management operations.

Not sure why I did not put those from start... Actually *not* having an
undo point here can be problematic, since undoing some previous action
was trying to restore from bad pointer (I think) in UI, generating
asserts.

Note however that it's not a 'pure' undo, in that you may not find your
linked data in exact same state as before deleting it, after an undo,
since it actually implies *reloading* the deleted libraries (and not
restoring from a previously stored memory dump).

Reported by @sergey, thanks.