Copy Scale: support copying arbitrary non-uniform scale as uniform.

Uniform scale is superior to non-uniform scale in that it works with
parenting without causing shear. Thus it is a valid desire in some
cases to turn arbitrary scale into guaranteed uniform scale.

Implementing this in the Copy Scale constraint allows one for instance
to 'inherit scale as uniform' by disabling Inherit Scale, and using
Copy Scale from parent with Offset and Make Uniform.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D5614

release/scripts/startup/bl_ui/properties_constraint.py

@@ -430,6 +430,7 @@ class ConstraintButtonsPanel:
         row.prop(con, "use_z", text="Z")
 
         layout.prop(con, "power")
+        layout.prop(con, "use_make_uniform")
 
         row = layout.row()
         row.prop(con, "use_offset")