Fix non-resumable binary uploads on Python 3

 1. Generator and StringIO are replaced by BytesGenerator and BytesIO.
    If BytesGenerator doesn't exist (as is the case in Python 2), fall
    back to Generator.

 2. BytesGenerator is buggy [1] [2] and corrupts '\r' into '\n'.  To
    work around this, we implement a patched version of BytesGenerator
    that replaces ._write_lines with just .write.

The test_multipart_media_good_upload has been updated to reflect the
change.  It is also stricter now, as it matches the entire request body
against the expected form.

Note: BytesGenerator was introduced in Python 3.2.  This is OK since the
      library already demands 3.3+.

Fixes #145.

[1]: https://bugs.python.org/issue18886
[2]: https://bugs.python.org/issue19003