Always queue antiexposes after flushing outstanding moves

Always queue antiexposes after flushing outstanding moves

If antiexposures are queued and then we do the outstanding moves
we will queue translations that will affect incomming exposes
wrongly wrt the antiexposure. So, make sure we process the outstanding
moves before doing the antiexposure.

Additionally this commit adds a bunch of comments about how the
expose handling works and fixes a small bug that made us always
flush outstanding moves a little to early than necessary.