exit, the destructor of an object instantiated in the global scope deleted
the vtkOutputWindow in use.  This was guaranteed to run before the program
completely exited, but may not have been run before the vtkDebugLeaks
classes were cleaned up.  To force the proper order of deletetion,
vtkDebugLeaks now holds a list of "cleanup" commands that are run right
before it reports any leaks.  The mechanism is now used to delete the
in use output window.