fix a small bug
  - wrong pthread key when creating master
modify lpel flag
Support Source/Sink tasks
   + an entity is mapped to a source/sink task if it is specified with a positive location, e.g. box@1 (this will be modified later to support more types of manual mapping)
   + a source/sink task is executed separately on its own thread (for more detail, see LPEL_FLAG)
- Update LOGFORMAT for centralQ approach
- Add LPEL_FLAGS for more detail of flag usage in LPEL
fix a typo
move LOGFORMAT and LPEL_FLAGS to snet-rts
bug:master must clean up the mailbox before finish
 - workers send requests to master after all tasks finished
 - master must clean up these requests in the mailbox before finish

small modification:
 - when a task finish, worker does not send it back to master
Merge branch 'centralQ' of git://github.com/nguyenvuthiennga/lpel into centralQ
Gna's version updated.. and sending one char is still working!!