Blender Git Loki

Fixes for some long standing transform bugs.

- [#6112] is this an extrusion bug?

When extruding, x-mirror was giving weird behavior since the extruded vertice could match with their non-extruded counterpart on the other side.

The solution is to disable x-mirror (with a transform context flag, like disabling PET) in that case.

- External constraint setup calls (BIF_*) didn't setup some internal structs properly.

For the user, this resulted in some transform (extrude particularly) showing a full 3d vector in the header instead of a scalar along the constraint axis (this messed up num input a bit too, you could type values in unused axis).