Big commit, but mainly adminstration.
- Enabled ot->flag OPTYPE_UNDO to work.
- Removed all redundant ED_undo_pushes, but I'd
recommend everyone to check it while testing. :)
- Added view manipulations as OPTYPE_REGISTER,
although this will flood the redo stack a bit...
Nevertheless; for a "redo last action" panel we
can simply check if both flags are set for redo.
- Bugfix in editmode undo: selectmode was cleared,
so you couldn't select after undo
- Bugfix in mixing tweaks and keymaps... solution
works but is weak, need to think over a while.
51ded6696a