Buttons: Prevent toggling disable hardware keys too quickly

* Apparently the phone window manager _really_ doesn't like it when you
  do toggle this too quickly.

Change-Id: I936c6554927ffcdc7c78edaf25f71aedba497ac8
Merge remote-tracking branch 'PA/kitkat' into legacy-staging

Conflicts:
	src/com/android/settings/cyanogenmod/ButtonSettings.java