Add `intersection(line segment, plane)' function.
Add `intersection(line segment, plane)' function.

Finds the intersection point for a line segment which crosses the
given plane.  Plane is currently specified by a normal; needs a
parameter for `D' to be added.

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@773 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok