hot-patch python requests 1.2.3 for Python 3.3

Python requests package 1.2.3 on Python 3.x has an issue when used with custom headers, and possibly only when sending binary data (data=b'bytes'). This hotpatches it, and works here in testing when I'm trying to set headers={'Content-Type': 'my-custom-content-type'} in the .post() call.

        from requests.models import PreparedRequest
        from requests.structures import CaseInsensitiveDict

        # hot-patch requests to avoid problem with
        def prepare_headers(self, headers):
            if headers:
                headers = dict((name, value) for name, value in headers.items())
                self.headers = CaseInsensitiveDict(headers)
            else:
                self.headers = CaseInsensitiveDict()

        PreparedRequest.prepare_headers = prepare_headers