Blender Git Loki

Bugfix #25652

Report was that move-to-layer menu failed. The real cause was
more complex; had to dive deep in the dungeons of the interface
code that handled undos and operators. Found several issues:

- popup menus (like redo operator, color picker) executed again
on a mouse-exit
- far too many buttons were sending undo pushes; even worse, in
the operator redo-panel each button action was pushed twice
- in case operator redo-buttons have own callbacks (like layer
buttons) the redo wasn't working
- layerbutton menu was called without creating a proper undo/redo
case

Things should all work smoother now!

On todo:
- better definition and handling of all versions for operator menus
(four types now, not fun)
also: make operator "do" menu, which on first action does operator
and then switches to redo-ing
- bring back Undo menu, to list the undo stack and jump in it.