DocumentManager: Use ICore::dialogParent for all dialogs

Change-Id: Id2eda57bc816c8601a3460aaf224852c267d336e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/coreplugin/documentmanager.h

@@ -153,7 +153,7 @@ private slots:
     void syncWithEditor(const QList<Core::IContext *> &context);
 
 private:
-    explicit DocumentManager(QMainWindow *ew);
+    explicit DocumentManager(QObject *parent);
     ~DocumentManager();
 
     friend class Core::Internal::MainWindow;