Optimized FlxOverlap

There's still one bug left, which I can't figure out. In flash, there seems to be some kind of memory leak : the memory size increases from 28.6 to 30.6 mb then drops back to 28.6 . This doesn't happen in any other platforms I tried, and I'm not really good with flash, so it would be great if someone could find this.

My future plans for this : 
-Rewrite the transformedUpdate() function. I think that the most optimal way would be to have an updated variable set at preUpdate to false, and when we do an overlap test, the functions checks if this variable is false, and if it is, calls the transformedUpdate() we have now.
-Maybe add masks now? I'm not sure if there would be a need for masks with overlaps, but I will add it if there is.
-Bug-testing.

After these, I will start working on the collision separation.