Peter M. Groen / FlashMQ

This fixes side effects when system time changes.

This performs a whole lot better.

Three parts to it:

- Start the app fresh per test. This avoids annoyances like getting
  retained messages on subscribe, messing up the test.
- Waiting for suback was apparently necessary.
- Because the Qt event loop was given time, waiting for publishes was
  sometimes pointless because it had already arrived. So, checking the
  receive list first.

Fix version bug.

Also include a few stats.

This was necessary for publishing will messages from the destructor of a
client, when you're connecting two clients with a will, no clean
session and the same ID.

Shifting signed integers is undefined and only sometimes produced
unexpected results.

Was detected in packet identifiers in QoS testing.

Also fixes not downgrading QoS on subscribe.

https://github.com/halfgaar/FlashMQ/issues/2

Unsubscribing paths that didn't exist caused creation of null nodes,
which subsequent use of the tree crashed on.

Found by quinox using AFL.