Client: when reconnecting, default to NT3. (#143)

Previously once the client fell back once to NT2, it would never try
connecting as NT3 even if the server was replaced with a NT3-capable
one.

Fixes #142.

src/Dispatcher.cpp

@@ -346,6 +346,9 @@ void DispatcherBase::ClientThreadMain() {
     conn->set_proto_rev(m_reconnect_proto_rev);
     conn->Start();
 
+    // reconnect the next time starting with latest protocol revision
+    m_reconnect_proto_rev = 0x0300;
+
     // block until told to reconnect
     m_do_reconnect = false;
     m_reconnect_cv.wait(lock, [&] { return !m_active || m_do_reconnect; });