Blender Git Loki

weight panel editing now supports mirroring
- use mirror when the option is enabled in editmode.
- fliped group names are used when they exist.
- only the setting that is edited will be applied to the mirrored verts group.
- copy value is applied to all mirrored verts of the selection.
- normalize normalizes all vgroups and mirrors.

utility functions defvert_sync and defvert_sync_mapped, similar to defvert_copy but does not remove existing groups and optionally creates groups as needed.
defvert_sync_mapped uses a an int array for mapping the flipped values.