improve size and positioning of Tabbable's after being torn off, hidden, reshown, etc

libs/gtkmm2ext/gtkmm2ext/window_proxy.h

@@ -87,6 +87,7 @@ class LIBGTKMM2EXT_API WindowProxy : public PBD::StatefulDestructible, public vi
 
 	void save_pos_and_size ();
 	void set_pos_and_size ();
+	void set_pos ();
 
 	virtual bool delete_event_handler (GdkEventAny *ev);
 

libs/gtkmm2ext/tabbable.cc

@@ -197,6 +197,7 @@ void
 Tabbable::make_visible ()
 {
 	if (_window && (current_toplevel() == _window)) {
+		set_pos ();
 		_window->present ();
 	} else {
 

libs/gtkmm2ext/window_proxy.cc

@@ -333,7 +333,7 @@ WindowProxy::set_pos_and_size ()
 	}
 
 	if (_width != -1 && _height != -1) {
-		_window->set_default_size (_width, _height);
+		_window->resize (_width, _height);
 	}
 
 	if (_x_off != -1 && _y_off != -1) {
@@ -341,3 +341,19 @@ WindowProxy::set_pos_and_size ()
 	}
 }
 
+void
+WindowProxy::set_pos ()
+{
+	if (!_window) {
+		return;
+	}
+
+	if (_width != -1 || _height != -1 || _x_off != -1 || _y_off != -1) {
+		/* cancel any mouse-based positioning */
+		_window->set_position (Gtk::WIN_POS_NONE);
+	}
+
+	if (_x_off != -1 && _y_off != -1) {
+		_window->move (_x_off, _y_off);
+	}
+}