Blender Git Loki

A couple of wee transform featurettes;

- center of rotation for camera in cameraview rotate has to remain the
camera center itself, drawing the dashed helpline then doesn't work,
since it's behind the camera clipplane. Just disabled that line.

- made MMB switch for cameraview grab to become quadratic, for a dolly
this feels OK, and makes it possible to move in small and large scenes.

- restored SHIFT modifier for translation and scaling. This based on old
convention that allowed precision editing on top of the transform you
already applied before pressing SHIFT.
Solved it with a new flag (T_SHIFT_MOD), since the G.qual cannot be
used. Transform() innerloop has to detect the SHIFT event itself.
Also coded it with storing the mouseposition while SHIFT event happened.
Hope Martin can approve! :)

- Martin's last commit made Manipulator Translate not work, it passed on
a zero translation to the constrainter, causing NaN's. Nicely catched the
exception.

- Fixed 'Trackball' to accept number input too