Better handle changing app transitions.

When we are in the middle of an app transition and need to change to a
new one we were not ending the old one in a clean state. Also,
wallpapers were defaulting to the wrong animation in certain
situations.

Remove ':' style iterators.

Fixes bug 6486708.

Change-Id: Ied17e8410486020295db380ff68df5dad08bc5cc