BGE Fix: [#19951] mouse over sensor is broken with letterboxing framing

BGE Fix: [#19951] mouse over sensor is broken with letterboxing framing

Tested with GameLogic.mouse.position and mouse over sensor.
It should be working with other mouse sensor as well. If not, please help to test and report a bug.
(couldn't test blenderplayer but it should be working there as well).

(Benoit, this is the same patch that I sent you. I hope it's OOP enough. Looking forward to hear from you on that)

I believe that this was the last "mouse" related bug we had reported. MouseLoook scripts should be working 100% in Blender/BGE 2.50 now \o/