Merge pull request #277 from mbuesch/assert_catch_warning

gui: Fix warning: catching polymorphic type by value

gui/application.cc

@@ -53,7 +53,7 @@ bool Application::notify(QObject *receiver, QEvent *event)
     bool retVal = true;
     try {
         retVal = QApplication::notify(receiver, event);
-    } catch (assertion_failure ex) {
+    } catch (const assertion_failure &ex) {
         QString msg;
         QTextStream out(&msg);
         out << ex.filename.c_str() << " at " << ex.line << "\n";