Updated M1A2 turret graphic to fix turret bustle glitch.  Rotation of
hull and turret are working properly.  Found out that in SP, they
transform the turret image such that the shadow always appears on the
side closest to the bottom of the screen (which explains the slightly
offset turret).  Won't implement this here, at least for now, as that is
a cosmetic issue.  Those bastards!  I'm learning their tricks!