Blender Git Loki

Woot woot commit.

Stencil style texture mapping. Ready for field testing and user feedback.

This commit adds stencil like brushes, like those that existed on old ptex branch.
(with the exception of clip colour)
To control the position of the stencil, you use

Q: translation
Shift - Q: scaling
Ctrl - Q: rotation

There's extra work that has been done to make this work:

* Support for coloured overlay in vertex/texture painting
* Also made A button do stroke mode selection like in sculpt mode,
when mask painting is inactive.

There are some TODOs to work on during bcon3:

* Support tiled and stencil mode in 2D painting. Support alpha textures also.
* Tidy up overlay code. There's some confusion there due
to the way we use the primary brush texture sometimes for alpha, other times
for colour control.

WIP design docs will be in

http://wiki.blender.org/index.php/User:Psy-Fi/New_Brush_Tool_Design