Add a redirect line to catch certain events

It's time to start noting certain events into the Apache log directly so we can trawl the logs later for information about when people leave openlibrary and where they end up. We should add a redirect line that writes an entry into the log, then bumps the person where they want to go. It should be super fast and hardly noticeable :)

In the first instance, we need to stamp some notes about Lending:

- Record the edition
   - Any/all downloads of IA loans; note the type of file (PDF or ePub)
   - Clickthroughs to OverDrive

Nice to have would be clicks through to any/all of the Read/Borrow/Buy options, but that can come later. We need to think carefully about what the redirect URL should be. E.g. - yahoo uses a rds.yahoo.com domain with lots of gobbledegook after the first slash. Ideas on this?

* Note that we don't care about *who* did it, just that it happened.