Atomic Edits Should be Undone Atomicly

[jmwright]

From a conversation with Ferdinand:
"Atomic edit operations should also be undoed atomically. E.g. when selecting a whole section to indent it with tab (good that that works), when I press undo (Ctrl+z) afterwards then it unindents the block line by line, so for a larger block I have to type a lot of undos. (In this particular case one can unident by selecting the block again and pressing shift+tab, but undo should also unident the whole block)."