Blender Git Loki

Fix T62706: Orphan Data : I have now to save a file, close and reopen it, only then I can purge previous deleted meshes.

libquery code has some specific handling for IDs tagged as 'no_main',
among which to never consider them as refcounted/refcounting other IDs.

This is fine, but it also means we have to be careful when moving an ID
from main to out-of-main status, to do all id remapping we need
//before// we tag it as no_main.

That was a bit tedious to track down, we'll have to be careful that all
the corner cases we have to take care of, do not end up in a giant soup
of expections to exceptions, where nobody can find its way anymore...