thorium: use message blocks in the worker-node route

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: add multiplexing in the worker-to-node route

thorium_message_multiplexer: original_message_count 13938274 real_message_count 1091403 (0.0783)
thorium_message_multiplexer: original_message_count 14713230 real_message_count 1182619 (0.0804)
thorium_message_multiplexer: original_message_count 14749892 real_message_count 1201124 (0.0814)
thorium_message_multiplexer: original_message_count 14825961 real_message_count 1201118 (0.0810)

time ./scripts/assembly_debugging/spate-saureus-fasta-gz-4x8.sh |tee log
real    1m32.063s

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>