windowclass when shutting down the video subsystem...this allows you to
 safely unload/reload the SDL shared library on Windows between
 initializations.

Discussion is here:
   http://www.devolution.com/pipermail/sdl/2005-February/067424.html

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extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401148