multiview: first attemp to get the right view used for the passes
This doesn't work! I think it is too late to set the camera, it needs to
be set before.

I'm thinking, a solution may be to run the whole thing once per view,
doing only the passes of the correct view.
multiview: exciting commit, multi view render working
...but
combined is still a problem, to be tackled next.
also anti-alias is not working (because ... dunno, probably because of
combined)

Anyhoo, it's time for a half-work celebration dance.
Merge branch 'multiview' of github.com:dfelinto/blender into multiview