Fix throttle test

This fixes the throttle test so that it clears the cache before running
the test and also pauses between HTTP requests. This reduces the
likelihood that it bumps into submitted responses from other tests. The
slight pause makes it pass consistently on my local machine.

Added a FIXME to look into the "pause" thing further because that's
total goofipants.
[bug 1072285] Update Django, django-nose and django-cache-machine

* update Django to 1.6.8
* update django-nose to latest in master because they don't like doing
  releases (b81f847)
* update django-cache-machine to latest in master because they don't
  like doing releases (f827f05)
[bug 1072285] Update django-adminplus

v0.3 of django-adminplus has fixes in it for Django 1.6, so this is
required.
[bug 1072285] Update requirements.txt file
Merge pull request #374 from willkg/1072285-django-upgrade

1072285 django upgrade