Update PR #224 with passing tests

Updates PR #224, with fixed tests.
It appears so:

    kafka-python $ python3
    Python 3.4.1 (default, Sep  3 2014, 10:12:05)
    >>> import struct, binascii
    >>> struct.pack('<i', binascii.crc32(b'abcd'))
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    struct.error: 'i' format requires -2147483648 <= number <= 2147483647

    kafka-python $ python
    Python 2.7.6 (default, Sep  3 2014, 10:15:09)
    >>> import struct, binascii
    >>> struct.pack('<i', binascii.crc32(b'abcd'))
    '\x11\xcd\x82\xed'