Stdout line splitting

This pre-splits a child process' output into individual lines, to make it easier for the jobtype to process.
This also implements your proposal from https://github.com/pyfarm/pyfarm-agent/commit/d9502780b8f4542a35e8acfc069800e11f5f82bb

If this way of doing this is okay, I will do the same changes for other handler methods in JobType.

Don't worry about this pull request when considering merging base_jobtype into master, I can easily just rebase it to master afterwards.