Fix unicode usage to make python3 work again

[bellini666]

No description provided.

[wkoot]

Build failing for Python 2.x

[bellini666]

@wkoot the fail doesn't seem to be related to my change. Also, without this change, python3 isn't working at all.

[wkoot]

It is related to your change; default behaviour for str(class) calls class.__repr__, but six.u(class) would call class.replace which is not there. See the following:

>>> class Blub(object):
...  a = 123
...  def __repr__(self):
...    return str(self.a)
...
>>>
>>> str(Blub())
'123'
>>>
>>> import six
>>> six.u(Blub())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/six.py", line 647, in u
    return unicode(s.replace(r'\\', r'\\\\'), "unicode_escape")
AttributeError: 'Blub' object has no attribute 'replace'

[wkoot]

This was cherry-picked from facebookarchive@2d5768b by the way.
Interesting that it's failing for you, a test case to show the error in travis would be really welcome.
I'm planning on packaging version 1.3.4 with some other fixes, this could be added if on time.

[wkoot]

Implemented in #16