Add a unique class ID for the bercon specific shade context
Add a unique class ID for the bercon specific shade context

Some textures in VRay get the shade context class id and if it is our
shade context - cast it to a specific internal class. If such a texture
is attached to BerconMapping texture it crashes when evaluating.

Bercon/BerconMaps,yavor-rubenov/BerconMaps,yavor-rubenov/BerconMaps,Bercon/BerconMaps