Fix issue #6319312: Consecutive call to Activity's onCreate()/onResume()...

...without onPause() in between

There was a bug in the handling of "always finish activities" where we
would go through destroying activities while in the middle of updating
the activity stack.  This would result in the activity behind the
non-full-screen activity being created and then immediately destroyed,
which things were not expecting.

Change-Id: Idaa89089f7b1af7eb747d7b8f9f394beeb2d23fa