Slightly altered the way Failures work to make them a whole lot more useful for jobs and plugins. A job can now specify a class name for which failure backend to use using the 'failureBackend' property. When none is set, the default failure backend will be chosen. Failures now also get passed the Resque_Job as the first argument instead of a custom payload. This to allow for custom values to be communicated from job (or plugin) to the Failure.