Original jobs code (from drake)
Changed the library to spark.app
Added test (changed main to defineTests).
changed comment in jobs.dart
Linted
Fleshed out comments.  Clarified parameter name.
renamed libraries
Added copyrights
cleaned up code and added newlines at end of files
consolidating _stream into _streamController (renamed _controller).
Clarified comment
refined comment and added void types to private methods
Merge pull request #492 from dart-lang/jobs

JobManager for long running tasks.