title: rgl toggle sharedMouse retrospectively
body: <p>rgl allows multiple subplots with <code>mfrow3d()</code>. These subscenes can respond to the mouse collectively with <code>mfrow3d(..., sharedMouse=TRUE)</code>.</p>
  <p>However, I would like to toggle the shared mouse behavior on/off <em>after</em> the the subplots have been drawn. Is this possible?</p>