a few small optimizations to reduce communication overhead
add size check on immediate messages
sent message pool allocator chunk size to a smaller value, which seems to work better for gups
change communicator context name to be less confusing outside the communicator
add communicator interface to support generic mpi requests
make grappa suspending barrier use communicator generic mpi requests
move to single, separate collective context to avoid deadlock
I think this works around the race when trying to use a GCE in SPMD mode in these tests
forgot to include this, but it should be unnecessary
Merge branch 'graphlabapi+mpi+collectives' into graphlabapi+mpi
fix local_iterate().size()
working MPI_Ialltoall using new generic MPI collective support