Rotation issue in perspective mode

[simonbethke]

This Video shows an issue with rotation when in perspective mode:

rotation.issue.mp4

Look closely at the mouse-position during rotation. I would expect the rotation marker (the line in the circle) to point always in direction of the mouse. So I can drag the mouse far away from the pivot to gain precision. This doesn't work currently. Even far away, the absolute amount of pixels on x or y that I move the mouse will translate directly to the rotation angle.

[slimbuck]

cc @kpal81xd