Feature additions in FlxWeapon & FlxSprite

Added some collision helper functions in FlxWeapon, and a setter for the "flipped" property on FlxSprite.

(in order to do this)
```
override private function setFlipped(isFlipped:Int):Int 
{
	if (isFlipped > 0)
		facing = FlxObject.LEFT;
	else
		facing = FlxObject.RIGHT;
	return super.setFlipped(isFlipped);
}
```

Also added number defines for Xbox 360 controller in Joystick.hx and made a crash prevention fix in FlxGroup.