Add triangle-clipping against a plane.
Add triangle-clipping against a plane.

The functions expect to take the full list of exported triangles,
and clips all of them in one go.  The return value is a new vector
which is the set of clipped triangles.

git-svn-id: 353be9ac11a1e711854a13efcc2fc17d9d6b83e7@774 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok