Blender Git Loki

BGE: undo view matrix scaling but keep axis inverting.

Previous commit 9d18fd11 introduced the possibility to scale the modelview
matrix by setting a scale on the camera but this caused undesirable lighting
and dynamic side effects.
This commit reverts the scaling effect but keeps the axis inversion effect,
which was the purpose of the first commit anyway.
A negative/positive scale on the camera is applied respectively as -1/+1 scale
on the modelview matrix.