[libcvd-members] SE2 + SO2?

[Georg Klein]

Does anyone mind if I add SE2 + SO2 to TooN and CVD(the bits for opengl)?
It's basically the SE3 code with all the `3's replaced by `2's (and the 
bits which need changing changed) and some of the esoteric stuff chopped 
away.

The reason I ask is because the functionality is pretty trivial, and could 
probably be implemented much more simply (cleanly?) than I have. Also it 
affects CVD too, because of where gl_helpers lives.