Django 1.5 compatilibity fixes

The changes in this pull request fixes issues issues relating to Django 1.5 compatibility.  The two issues are:

- All templates are using the old (pre-1.3) Django url template tag syntax.  The change is described in the Django 1.3 release notes here:

https://docs.djangoproject.com/en/dev/releases/1.3/#changes-to-url-and-ssi

I've updated all use of the url template tag so it conforms to this.  Unfortunately this means that Django 1.2 compatibility is broken in the process.

- URLValidator no longer provides the `verify_exists` keyword argument in Django 1.5.  From reading the docs, I see that Django 1.2 - 1.4 had this default to `False` anyway, so I've removed this keyword argument.

Because of these changes I've also updated `setup.py` to indicate that it is compatible with Django 1.3 and later, and no longer incompatible with Django 1.5.

Tests are passing locally, with the exception of `redis` tests (I do not have Redis setup locally to use it).