Prior to this patch the effect of applying the "Shade Smooth" object operator and the value of "Vertex > Auto Smooth" were lost when changing an existing bolt (via context-menu's "Change Bolt").

This patch preserves both.

A simple heuristic is used to detect if "Shade Smooth" has been used: the value of use_smooth of the first polygon in the mesh (prior to activating "Change Bolt"). Experiment has shown that "Shade Smooth" / "Shade Flat" are equivalent to setting use_smooth to True/False (respectively) on every polygon in the mesh.

(No heuristic is needed for Auto Smooth, as it is a top-level property of mesh data blocks)