Timezone aware

I made the timezone aware issue compatible with django 1.3

Basically, I try to import django.utils.timezone and when it fails, it falls back to datetime.datetime

I had to import timedelta directly when needed, i.e., from datetime import timedelta in order to use datetime as before.

I also made the use of dateutil optional. It if's not present, it will fall back to strptime. What I don't really like about this, is that the timezone is hardcoded (+0000). dateutil will detect the correct timezone.

I would like to add some tests to make sure that all the importerrors fall back to the original state, but I could not find a way to impose the ImportError (like using mock library). Any ideas on how to do this?