Cleanup and repair multi-window support

Conflicts:
	core/java/android/app/Activity.java
	core/java/android/inputmethodservice/InputMethodService.java
	packages/SystemUI/src/com/android/systemui/recent/RecentsPanelView.java
	services/java/com/android/server/am/ActivityManagerService.java
	services/java/com/android/server/am/ActivityStack.java
	services/java/com/android/server/wm/WindowManagerService.java