keep the resulting tm_event_t that is generated because the back-end
TM library actually caches a bunch of stuff on it for internal
processing, and doesn't let go of it until tm_poll().
tm_event_t's are similar to (but slightly different than)
MPI_Requests: you can't do a million MPI_Isend()'s on a single
MPI_Request -- a) you need an array of MPI_Request's to fill and b)
you need to keep them around until all the requests have completed.
This commit was SVN r10820.