Support for New Relic wrapped applications

I've been trying to get RQ working on Heroku lately, and was hitting pickling errors related to instancemethod's.  After some digging I found that New Relic's analytics system uses an object wrapper around a lot of objects and it was causing RQ to fail to identify the incoming instance methods for serialization.

This patch fixes the issue by type checking `func` and extracting the actual method from the object wrapper.

I realize it might be too much of a hack for you to want it in the main repo, but I thought I would submit it in case there is some interest.