Blender Git Loki

Bugfixes for quit.blend + library linking, the last commit didn't solve
that completely:

* quit.blend is saved from the undo file, which did not save out library
ID_LI and ID_ID blocks, for quick undo keeping the library datablocks.
However this means library links are lost on reading the quit.blend, so
now instead of not writing them, they are not read on undo.
* Libraries were not not using the right path yet always.

Note the screen setup is still not recovered from the quit.blend if no
auto save happened yet, but that is not important enough to spend time on
now.