remove annoying warning
fix crash on < iOS 7
Add overlay view to windows at valid levels

See https://github.com/TransitApp/SVProgressHUD/issues/295
Fixing background mask

This is a fix for the background mask misalignment issue referenced here: https://github.com/TransitApp/SVProgressHUD/issues/342 , with the specific fix recommended by @Tokanod
fixing TransitApp#342 - when rotating while the progresshud is visible, the background and the hudview are positioned correctly
Revert "Add overlay view to windows at valid levels" as it causes the progress hud not rotating correctly after the keyboard has appeared and disappeared once

This reverts commit c7e801a4e017f461e1f7a330e0a6ad4f8d70c81d.