Fixed fallback imports for django.conf.urls.defaults

I corrected the issue I mentioned here:
https://github.com/toastdriven/django-tastypie/pull/839#issuecomment-21372790

Most fixes were done by importing the needed items from django.conf.urls. 

In a few of the tests, the relevant imports were unnecessary, so I removed them. 

Also, the fallback comment should be for <1.4, not <=1.4.