Add template dropdown sensitivity

...for those who select a template but forget activate the checkbox and
wonder why it doesn't work :)

gtk2_ardour/session_dialog.cc

@@ -611,6 +611,7 @@ SessionDialog::setup_new_session_page ()
 
 	HBox* hbox4a = manage (new HBox);
 	use_template_button.set_label (_("Use this template"));
+	use_template_button.signal_toggled().connect(sigc::mem_fun (*this, &SessionDialog::template_checkbox_toggled));
 
 	TreeModel::Row row = *template_model->prepend ();
 	row[session_template_columns.name] = (_("no template"));
@@ -649,6 +650,14 @@ SessionDialog::setup_new_session_page ()
 
 	session_new_vbox.pack_start (*vbox2, false, false);
 	session_new_vbox.show_all ();
+
+	template_checkbox_toggled ();
+}
+
+void
+SessionDialog::template_checkbox_toggled ()
+{
+	template_chooser.set_sensitive (use_template_button.get_active());
 }
 
 void

gtk2_ardour/session_dialog.h

@@ -181,6 +181,8 @@ private:
 	Gtk::CheckButton use_template_button;
 	std::string load_template_override;
 
+	void template_checkbox_toggled ();
+
 	void more_new_session_options_button_clicked();
 	void new_name_changed ();
 	void new_name_activated ();