The method used by Commons IO to get the available disk space fails on
Android devices that lack a df binary - use the Android API instead.

This removes the other projects' dependency on the Android API.

See issue #3612607.

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

CryptoExecutor and DatabaseExecutor now use bounded thread pools with
unbounded queues, since running too many tasks in parallel is likely to
harm performance; IncomingConnectionExecutor, PluginExecutor and
ReliabilityExecutor use unbounded thread pools with direct handoff,
since their tasks may run indefinitely. There are no longer any bounded
executors, and all executors discard tasks when shutting down, which
fixes issue #3612189.

Responsibility for starting and stopping services has been moved from
BriarService in briar-android to LifecycleManagerImpl in briar-core.
However, BriarService is still responsible for stopping the
Android-specific executors, which is ugly. It would be better if
executors registered themselves with LifecycleManager.

Android doesn't currently store bundles persistently, so it's premature
to protect against accidental information leaks through persistent
bundle storage. Protecting against deliberate information leaks by the
OS is probably futile, so there's currently no need for bundle
encryption.

Only the ARM binary is included at present. Better control of the Tor
process is needed - it's possible for it to be left running when Briar
exits, and if the cookie file is deleted it's no longer possible to stop
the process.

The UI may access the DB in response to UI or DB events; to maintain a
consistent view of the DB's contents, the tasks performing these
accesses must be prevented from overlapping, and must produce consistent
results if reordered. A single-threaded executor and latches are used to
prevent tasks from overlapping, without blocking non-UI access to the
DB.

Mutable static fields should be avoided, but this is the only way to
make the bundle encrypter available before calling
RoboActivity.onCreate(), which needs to be passed the decrypted state.

Only the bundle contents created by Briar classes are encrypted.

This should make it possible to develop the core in Eclipse without the ADT.

The project is now built as an Android project (via Eclipse or
ant). Tests have been moved to a separate project so they can exist
outside the Android build process. A basic Android app structure has
been created. A Bluetooth plugin for Android has been added, and the
Bluetooth plugin for J2SE has been modified to use the same techniques.