Blender Git Loki

Bugfix #21028

- Image Editor, "New", gave for each tweak in redo menu a new Image
when Object is in Editmode. This is a limitation of our current
undo system. Marked this issue in the wiki todo.
Solved by adding a poll in operator that prevents this to be called.
(a bit annoying, but the error is worse!)

- On assigning a new image texture to faces in Editmode, no redraw
happened in 3D window. Added notifier for it.