Note: There are not any uses of this logger in the core CMS, so this one is either going to have to rely on unit tests & code review or I'll have to spend time writing an extension just to make this testable.
JLogLoggerCallback verifies that is has a callback and it is callable in its constructor and throws an exception if these conditions are not met. The problem here is that we do not have a JLogException exception, nor was the error condition unit tested. This PR addresses that.
Merged on review