Hmm, maybe looking at diff is somewhat confusing or I'm missing something. It's neither failing back nor making typo will make it silently set something. It just sets `@backend` to default one (`Failure::Redis`) if it's nil. So if somebody won't set custom backend (by `Resque::Failure.backend = Resque::Failure::Backend`), then `Failure::Redis` will be set. Also, if somebody will make a typo in class/module name, than ruby will throw exception.

So, should we a) log message that user didn't set `Failure.backend` and inform that Failure::Redis was set, b) Should we this name error? I'm not even sure it it's possible, ruby will throw NameError when trying to set backend as a class name with typo.

I might be wrong though. What do you think?