Use a user-agent other than the httplib2 default.

There is something about the default httplib2 user-agent that causes some web
servers to throw up.

Try this, for example::

    >>> import httplib2
    >>> h = httplib2.Http()
    >>> response, content = h.request(
    ...   "http://ankursinha.in/blog/feed/")
    >>> response.status
    406
    >>> response, content = h.request(
    ...   "http://ankursinha.in/blog/feed/",
    ...   headers={'user-agent': 'trololololololol 9000'})
    >>> response.status
    200