The Tor plugin tests are consistently failing with the latest versions
of Silvertunnel and Spongy Castle; we may need to ship native Tor
binaries for Windows/Mac/Linux and use Orbot on Android.

Fields in Android UI objects that are accessed from background threads
must be declared volatile. UI objects use data attached to DB events to
avoid DB lookups, which complicates the UI code but should improve
performance.

Generate a random UUID instead of using a fixed UUID. Close sockets when
exceptions are thrown (not doing so can cause problems with subsequent
sockets on Android). Use a semaphore with tryAcquire() instead of a lock
when making alien calls, to avoid possible deadlocks.

Only the bundle contents created by Briar classes are encrypted.

This limit is necessary to limit the size of subscription update
packets; it can be lifted when incremental subscription updates are
implemented.