do not both fail and retry the job if it fails before perform

After forking, but before perform is called, the job will be scheduled for retry, but will also bubble up to the failed queue.  A manual replay at that point, could be disasterous.

A detailed discussion of the problem can be found in #97, specifically here: https://github.com/lantins/resque-retry/issues/97#issuecomment-41448307

Will add a few comments to the PR on the code.

This has not been vetted in production, but I'm opening this up to get comments