Updated translate_url to reverse unnamed urls

Stephen,

This request is in response to https://github.com/stephenmcd/mezzanine/issues/1066. The tags work on the main admin page, and it fixes the issue at django-widgy. I am concerned about nesting try statements. Do you have any ideas on how to make this prettier? Also, does it mess up any edge cases? I tested this on django 1.4.11. 

Zach