glsl: Use the new shader abstraction layer.
glsl: Use the new shader abstraction layer.

At least in the new paths for loading multiple shaders; a few
other places as well.

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1509 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok