added non robust messages.

Ignore-this: 6c83819c79025174e10c159107e297ef

Some messages you don't care if they get delivered. For example doing audio streaming
a loss of message isn't the end of the world.

So now messages can be sent that are not robust that don't require an ack.

darcs-hash:20140709132213-c21fe-f24e1402fed3c48e325e0989be7a7ac006db28ae
added "not_robust" function to expose functionality to apps

Ignore-this: aee05256a4ec0df0bb958a88b659817

Apps can set a message to be not_robust which doesn't guarantee delivery.

darcs-hash:20140709132419-c21fe-352772fc1c63b1475e0cf4fd84dacf8a7d94975c
fixed bug in counting queued and in flight non robust messages

Ignore-this: 3af49f4049dc8186f8d7dd91e44b2a77

darcs-hash:20140709142647-c21fe-478991610846332312e13b63cca57b5d8aa2dd8c
now cleanup of messages that are not robust happens less lazy.

Ignore-this: b7ef7b81735bf7e6302e27d39d7950ed

Better to cleanup sooner than every three seconds. More predictable performance.

darcs-hash:20140709185932-c21fe-acc38b5e3be7609ff5acd858867841e11ef3eb28