base

Return to recents when coming from recents

If a task is launched from recents then backing all the way
out of the task will return you to recents. Entering the task
in any other way (home, another activity, nav bar) will reset
this behavior.

Fixes bug 15703876.

Change-Id: I98dc36e4dbcb238d59e2175832076de7225bfdd9