Fixed coordinate axes rendering artifact on both mac/windows.
Fixed coordinate axes rendering artifact on both mac/windows.

Prior, triangles renderered *first* would be rendered on top of other
geometry, regardless of z-depth.

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@2489 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok