Validate some cases using G_MAIN instead (I don't think we want to work
on any other Main than G.main one when registering/unregistering nodes
etc.).
And when freeing, all ID not in Main shall now be tagged accordingly, so
we *should* not need to do that stupi search over all ntrees in G.main
to check wether we have to free it ourself or not!
fd48e685c3