Add method _log() to jobtype API
Add method _log() to jobtype API

This method can be use by a jobtype implementor to inject messages into
the task log. This is useful for debugging jobtypes. The injected
messages will be logged as coming from the pseudo stream "jobtype".

guidow/pyfarm-agent,guidow/pyfarm-agent,guidow/pyfarm-agent,pyfarm/pyfarm-agent,pyfarm/pyfarm-agent,pyfarm/pyfarm-agent