Blender Git Loki

Large fix for multires. Changed UV coordinates (MTFaces) to be special first-level data in multires. The data is now stored in a standard CustomData struct in Multires, rather than being stored for each level. (The UVs can now only be edited on level 1.) Changes allow multiple sets of UVs to work correctly. This change should also decrease multires memory usage some (though only when UVs are being used, of course.)

Changes to CustomData:
Some functions would only return the current active layer, added extra variants that take an index to select the level (modeled after CustomData_get_layer_n.)

Still todo:
* UVs are being interpolated linearly, should probably offer Catmull-Clark subdivision like Subsurf modifier.
* Vertex Colors still don't support multiple customdata layers.
* Editing UV data on levels other than 1 should be disabled in the interface (same for weights)