"synchLock" will become confusing when we have lots of objects with "sync" in the name.

- replaced use of Object instance mutex with a private final Lock object
- replaced Object signaling with specific condition signalling

DuplexOutgoingSession flushes its output stream if it's idle for a
transport-defined interval, causing an empty frame to be sent. The TCP
and Tor plugins use a socket timeout equal to twice the idle interval to
detect dead connections.

See bugs #27, #46 and #60.

We don't need two separate executors for long-running IO threads.

This may have been the cause of bug #69. Removed the wait-for-shutdown
code in DroidtoothPlugin that was added to attempt to avoid that bug.

This should enable us to connect to contacts faster at startup and
whenever a new means of connecting becomes available.

Very important stuff.

All JVMs must support UTF-8 encoding.