- change mesh_get_derived_render to mesh_create_derived_render (always

builds new DerivedMesh... caching can come later)
 - split DerivedMesh returning functions into editmesh and mesh groups
 - got rid of DL_NORS displist type (get built on fly for mesh when
   needed)
 - got rid of Mesh.disp (yay!)
 - started to punch DerivedMesh returning functions into shape to introduce
   modifier stack

source/blender/python/api2_2x/NMesh.c

@@ -2399,7 +2399,6 @@ static void EXPP_unlink_mesh( Mesh * me )
 
 static int unlink_existingMeshData( Mesh * mesh )
 {
-	freedisplist( &mesh->disp );
 	EXPP_unlink_mesh( mesh );
 	if( mesh->mvert )
 		MEM_freeN( mesh->mvert );