Both devices try to make outgoing connections and accept incoming
connections simultaneously. This should lead to faster connection
establishment when there are asymmetrical connectivity problems, such as
devices that are unable to receive LAN multicast packets or make
themselves discoverable via Bluetooth.

See issue #development-tasks/20: some devices can send but not receive
multicast packets.

This should improve durability in the case of a crash (see
http://www.h2database.com/html/advanced.html#durability_problems). The
performance penalty for H2DatabaseTest is roughly 10%.

We always use transactions so auto-commit can always be false.

Various thread safety fixes, saner use of exceptions, and code
reformatting. The Tor plugin now creates a single control connection at
startup and closes it at shutdown. Fixes issue #3611962.

See issue #3612607.

Both sides now close the connection after exchanging confirmation
results unless both results are positive.

Some Android devices require a lock to be held while using multicast, to
disable the packet filter that normally filters out multicast packets.

Fixes issue #3611924.

Partially addresses issue #3611924.

Fixes issue #3612299.