Fixed a Python 2.6 regression (GzipFile can't act as a context manager)

# based on Python 3.3's gzip.compress

def gzip_compress(data):

    buf = io.BytesIO()

    with gzip.GzipFile(fileobj=buf, mode='wb', compresslevel=0) as f:

    f = gzip.GzipFile(fileobj=buf, mode='wb', compresslevel=0)

    try:

        f.write(data)

    finally:

        f.close()

    return buf.getvalue()