Include size of sequence in topics

Might be helpful for automatically detecting sequences, doesnt' cost
anything.
subscriber: support expected client count

And do proper per client missing/duplicate stats
publisher: Add rate limiting support

This makes it easier to test at a predictable and controllable message
rate, rather than "as fast as possible"

Example output (after appropriate ulimit modifications)
 # Start listener
python malaria_subscriber.py -n 1000 -N 500

 # Start 500 separate processes publishing 1000 msgs at 5 / sec
python malaria_publisher.py -t -n 1000 -P 500 -T 5

Subscriber output

Clientid: beem.listr-2587
Total clients tracked: 500
Total messages: 500000
Total time: 205.17 secs
Messages per second: 2437 (0.410339 ms per message)
Messages duplicated: []
Flight time mean:   994.66 ms
Flight time stddev: 414.01 ms
Flight time min:    3.24 ms
Flight time max:    2058.29 ms
subscriber: detect dropping and abort test

If messages are being dropped, there's a near certainty that the test
will simply never complete, so just abort.