Blender Git Loki

Cleaned up new constraint line drawing while grab/rot/scale

- uses callback mechanism to tell main drawing routine what to do
- for that reason it doesn't use frontbuffer drawing anymore
and it shows up in all 3d windows as well
- it uses the same colors as for the grid axes (I tweaked it a bit,
this is based at themecolors, and also should work in different
background and grid color)
- I disabled drawing lines through every object or every vertex.
The current display method is clear and not distracting
- when in 'local' transform (double press X/Y/Z), it displays a nice
axis in the center of transform for vertices.
In object-mode, local transform differs per object, so constraint lines
and axes are drawn for each individually...

Also:

- fixed an old bug in rotate transform(). Using a constraint for
rotation (X, Y, Z) didn't work for multiple objects at all!