Obj: make mtl importer accept kd, ks etc. as well (Kd, Ks being the correct form). This is for keeping up compatibility with assimp's own Obj exporter, which has been inaccurate about this since inception.

code/ObjFileMtlImporter.cpp

@@ -129,6 +129,7 @@ void ObjFileMtlImporter::load()
 	{
 		switch (*m_DataIt)
 		{
+		case 'k':
 		case 'K':
 			{
 				++m_DataIt;