Patch Set 12: Looks good to me, but someone else must approve

I am not sure whether we can solve proper handling of mode changes with our previous attempts to add more if-clauses to the already complicated DirCacheCheckout. So I propose this different attempt: Whenever we test for content equality during checkout we should always look at contentID and file-mode together. There is no case in the current implementation where we should decide differently whether a change is on file-mode or on content.

I also removed the dependency of this proposal to change 4958 (yes, I know, I introduced the dependency). I am not sure whether we want 4958 - but this change is definitely required.