Blender Git Loki

Change in behavior to shrinkwrap modifier's offset value with negative enabled.
- negative ray casts would invert the offset direction.
this meant if positive and negative were enabled at once and the mesh was slightly inside & outside the object it wrapped,
the offset would be applied in opposite directions.
This way the offset is always along the vertex normal.

- allow negative offset from RNA, could be useful and no benefit to disable.