Let the plugin determine whether to flush the output stream after each

api/net/sf/briar/api/plugins/Plugin.java

api/net/sf/briar/api/protocol/ProtocolWriter.java

api/net/sf/briar/api/protocol/ProtocolWriterFactory.java

api/net/sf/briar/api/transport/BatchTransportWriter.java

...net/sf/briar/api/transport/StreamTransportConnection.java

components/net/sf/briar/plugins/AbstractPlugin.java

...nents/net/sf/briar/plugins/bluetooth/BluetoothPlugin.java

...briar/plugins/bluetooth/BluetoothTransportConnection.java

components/net/sf/briar/plugins/file/FilePlugin.java

...onents/net/sf/briar/plugins/file/FileTransportWriter.java

...nents/net/sf/briar/plugins/file/RemovableDrivePlugin.java

...nents/net/sf/briar/plugins/socket/SimpleSocketPlugin.java

components/net/sf/briar/plugins/socket/SocketPlugin.java

...et/sf/briar/plugins/socket/SocketTransportConnection.java

...ents/net/sf/briar/protocol/ProtocolWriterFactoryImpl.java

components/net/sf/briar/protocol/ProtocolWriterImpl.java

.../net/sf/briar/protocol/batch/OutgoingBatchConnection.java

...et/sf/briar/protocol/stream/IncomingStreamConnection.java

...et/sf/briar/protocol/stream/OutgoingStreamConnection.java

...onents/net/sf/briar/protocol/stream/StreamConnection.java