Support Source/Sink tasks + fix bugs
- Modify glue_snet.c to support source/sink tasks
- Fix small bug in collector.c (the sync rec should be sent only when
  the ready stream set is empty --> otherwise, it may forward unexpected
  sort end. This happens when there is initial branches mixed with
  non-initial ones.)
- Implement SNetStreamGetId for debugging (not support for pthread
  back-end)
- Modify mon_snet to obtain log files for source/sink and wrappers
- update LOGFORMAT