Dweller 1.24.16

Quick release to fix music playback issues and the dreaded crossbow on edge of map bug (again!)

#670 Fix Halberd attack

#669 Fix crossbow issue again

#668 Make sure to pause the music when application is put in the background

#667 Fix spell backfire chance of some items 

Source and comments: http://www.dwellergame.com/2013/04/dweller-12416.html