Update context_processors.py

Remove obsolete documentation.
Merge branch 'master' into next

* master:
  Update context_processors.py
Stop adding methods to admin_cls, this does not work with LegacyExtension under certain circumstances
Add support for Python 3.3 (successfully run the testsuite at least)
tox.ini: Also run the PY3 tests with Django 1.6 and 1.7
Reorder the envlist in tox.ini