Updating a view used to cause the view to render. Now, rendering the
view causes the view to update. This simplifies making sure views are
up-to-date, but required some changes.

 - ClientGeoView/2D plugins now execute Render on the view instead of
   Update.

 - ClientGeoView/2D Initialize() warning is now fixed.

 - vtkCommand has a new event (ComputeVisiblePropBoundsEvent). This is
   called when vtkRenderer::ComputeVisiblePropBoundsEvent is called.
   vtkRenderView now listens for this event, along with vtkRenderer's
   StartEvent, so it can catch (almost?) all indications that the
   pipeline is about to be updated. vtkRenderView (and all its
   representations) now correctly update before pipeline updates.

 - Some geovis tests needed to be updated to make sure the view is
   rendered correctly with these changes.

 - vtkGeoView/2D need to call superclass's PrepareForRendering.

 - vtkConvertSelection had some memory bugs, and was not handling all
   cases correctly.

 - vtkRenderView subclasses needed to be more careful about making sure
   pipeline is valid at every stage, including when the selection
   connection is temporarily NULL.

 - vtkView no longer has the hack that calls Update on representations
   before they are added to the view.