Defining a logger

Note, the TODO in the spec test.  That line is not passing and I have no idea why.  I was trying to find a nice way of just including a `logger` method just once somewhere, but I'm only able to do this way.  Since it's used in classes and modules, I have to use `self`.

Can anyone think of a better way to do this? @jcoyne @mjgiarlo @jeremyf 
I suggest:

```
@@log ||= ActiveFedora::Base.logger || ::Logger.new(STDOUT)
```