Blender Git Loki

AnimSys2: Bone Roll Issues

In this commit, I've attempted to improve the situation of bone roll problems that occur with the recalculate bone roll tool, and also when extruding/moving bones under certain conditions.

What's changed:
* When transforming bones, as part of the recalculations done on every update, the roll of bones who have their tip selected will be recalculated using the 'z-axis up' method. Reported by Glenn Melenhorst on BA.org

* Split the 'z-axis up' and 'align z-axis to cursor' roll recalculation methods into separate functions that can act as callbacks. Refactored the auto_align_armature() function to support this. It was needed for the first major change to occur.

* As an experiment, I've changed the final step of the z-axis method to use mat3_to_vec_roll instead of atan2 directly. It currently seems to work better, but I'm not totally sure yet. Will check on this again another day...