When the classes in wave.py opened files themselves, their .close() methods

When the classes in wave.py opened files themselves, their .close() methods
didn't bother to close the files.  This caused the new test_wave test to fail
under Windows, as Windows won't let you delete a file that's open.  Fixed
that by ensuring the wave read & write classes' .close() and __del__ methods
close files that were opened by their constructors.