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 branch 'kitkat' of github.com:AOSPA-legacy/android_packages_apps_Settings into kk4.4