didn't import it.  Also got rid of some inconsistent spaces inside
parentheses in test_gzip.py.

and replaces them with a new API verify(). As a result the regression
suite will also perform its tests in optimization mode.

Written by Marc-Andre Lemburg. Copyright assigned to Guido van Rossum.

test file, too, so the methods have more work to do.

writes a chunk of compressed data, closes it, writes another chunk, and
reads the contents back to verify that they are the same.