Merge branch '235-transport-key-manager-deadlock' into 'master'

Avoid potential deadlock in TransportKeyManager. #235

See rambling description on the ticket and in the architecture channel...

Fixes #235.

See merge request !79

briar-api/src/org/briarproject/api/db/DatabaseComponent.java

@@ -28,6 +28,10 @@ import java.util.Map;
 /**
  * Encapsulates the database implementation and exposes high-level operations
  * to other components.
+ * <p>
+ * This interface's methods are blocking, but they do not call out into other
+ * components except to broadcast {@link org.briarproject.api.event.Event
+ * Events}, so they can safely be called while holding locks.
  */
 public interface DatabaseComponent {