for events, the slug and event_id can come in either order in the URL

e.g.,  All the following will go to the same place without error:
http://everybodydrink.com/event/45
http://everybodydrink.com/event/45/flyers_vs_penguins
http://everybodydrink.com/event/flyers_vs_penguins/45
http://everybodydrink.com/event/flyers_vs_penguins/45/foo/bar