Pass 'current_app' when rendering view names

Hey,

Currently the breadcrumbs don't utilize `current_app` when reversing view names. This can lead to unexpected results when using namespaced URLs.

With this commit, `current_app` is figured out from the request object and passed to `reverse`.

Tested and works on Django 1.5. I didn't have a pre-1.5 codebase handy, but that AttributeError exception handler should cover them. Feel free to test/tweak as needed.

Thanks.