Fix T55958: allow the user to select between spring and spring2.

The old springs with damping 1.0 operate in a special way that
is more similar to plastic deformation than a spring. Some users
rely on that, so let the user choose which implementation to use.
This also restores full backward compatibility with 2.79.

Reviewers: sergof

Differential Revision: https://developer.blender.org/D3544

release/scripts/startup/bl_ui/properties_physics_rigidbody_constraint.py

@@ -140,6 +140,11 @@ class PHYSICS_PT_rigid_body_constraint(PHYSICS_PT_rigidbody_constraint_panel, Pa
             sub.prop(rbc, "motor_ang_max_impulse", text="Max Impulse")
 
         elif rbc.type in {'GENERIC', 'GENERIC_SPRING'}:
+            if rbc.type == 'GENERIC_SPRING':
+                row = layout.row()
+                row.label("Spring Type:")
+                row.prop(rbc, "spring_type", text="")
+
             col = layout.column(align=True)
             col.label("Limits:")