Re-enable PaRSEC backend profiling, and extend it to comms.

All change are in the parsec backend:
 - Remove the compile-level PARSEC_PROF_BACKEND which had to
   be defined/undefined by hand in the code
 - Port old profiling style to new profiling style
 - Create a send_msg function that does all the book-keeping
   when doing a parsec_ce.send_am from TTG; use only that function
   from the rest of the code
 - Extend the backend profiling events to log communications