Nightly Binary Distribution Build
Tests: 739 passed
Duration: 6 minutes
Changes: Who: Florian Schmaus
Why: Use standard stanza listeners in MultiUserChat
Those, relatively new, listeners guarantee that the individual
listeners are not invoked in concurrently while preserving the
order. Exactly what MultiUserChat previously did with AsyncButOrdered,
which is now no longer needed and hence can be removed.

Who: Florian Schmaus
Why: core: improve AsyncButOrdered
Instead of marking the handle as not running by setting the handler"s
value in the map to false, we now remove simply the key if there is no
handler running. This also means we no longer need to use a weak hash
map for this.

Also reduce the size of the synchronized blocks, mainly by scheduling
the handler outside of the synchronized(threadActiveMap) block.

Make some code better readable and add some more comments. Also do
start a new handler thread if the task threw.
Changes by Florian Schmaus