Android denial of service attack using class 0 SMS messages

Bug 9702645
Bug 11970403 - Change to ClassZeroActivity to singleTask

Cherry pick the change from master.

Making every AlertDialog immediately visible can lead to exhaustion
of graphics-related resources, typically memory, resulting in a
broken bufferqueue/hw renderer, and subsequent system crash.

Make ClassZeroActivity a singleTask activity, and queue incoming
messages if one is already being displayed.

Change-Id: I0aef7b857364acc404e79581ba5e503571065483
Revert "ClassZeroActivity: Queue messages instead of displaying them all at once (take 2)"

This reverts commit 4eb44c148309905e497f81ee7130af474d98c388.
Merge tag 'android-4.4.2_r1' into kk4.4

Android 4.4.2 Release 1

Conflicts:
	src/com/android/mms/ui/ClassZeroActivity.java