Blender Git Loki

Fix T66641: Certain drivers fail to copy when copying a full scene.

The core of the issue here is that 'make single user' functions still
does its own, manual and quite partial, remapping of IDs, which covers
all most common cases but cannot consider *all* possible ID usages
(especially when it comes to drivers or custom properties, that can
essentially point to any kind of data-blocks).

This fix is merely a band-aid, there is no way to fully solve this
without a complete rewrite of that area of code to make use of modern ID
management code.