Tidy up some of the C#-shader joining code.
Optimise shadow rendering with cached non-shadow stencil buffer and optimised Clear() call. Up to 20% faster with shadows.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@270 a9f3cfff-6c41-7446-b0ca-052bd761e6eb