1.fix comments errors
Allow for there being no "errors" in the twitter api response.

When a successful "user" query to the twitter api is completed the json that is returned is a list.
In order to validate the response the code tests to see if it was a dictionary with an "error" key.
However passing a string as a index to a list will raise a TypeError, which was not being caught by the "except" clause.

I have added TypeError to the list of items being caught. There are of course other ways of verifying the response but I think just adding the TypeError is in keeping with what you have already done.

For reference, here is what I was seeing:

> python manage.py poll_twitter --traceback --force
Traceback (most recent call last):
  ...
  File "/.../lib/python2.7/site-packages/mezzanine/twitter/models.py", line 74, in run
    raise TwitterQueryException(tweets["errors"][0]["message"])
TypeError: list indices must be integers, not str
Added David Higgins to AUTHORS
Merge.
Merge.
Added hanchen to AUTHORS.
Fix tag cloud factor in generic app.
Version bump to 1.4.13
merged with upstream

Merge tag '1.4.13'