Blender Git Loki

Some refactoring of the Mesh conversion code to make things easier to read. Material conversions are now also cached so they do not have to be redone per face. This results in about a 35% improvement in conversion time in scenes with a lot of faces. I'm keeping the old mesh conversion code around as BL_ConvertMesh_old() for further benchmarking/comparisons. It will need to be removed prior to being merged into trunk.