Simple Test program for asynchronous unbuffered mailbox.
Roger Pearce -- 2011.03.01

Uses MPI_Isend and MPI_Irecv to exchange messages from
all-to-all in a random pattern.  

Compiling:
Edit 'make_me.sh' and set MPICXX and BOOST_INCL as approperate.
Only Boost header files are needed, tested on Boost 1.33 and 1.45


Usage:
atlas608@pearce7:srun -n8 -ppdebug ./test_mpi_mailbox_unbuffered 100
Sending 100 unbuffered messages using 8 processes
Elapsed time = 0.000259, Message rate = 386100 Messages per second



WARNING: Overflows can occur if MPI eager sends get too 'eager'.