Fix external file change notification in case of multiple windows.

The notification was only done when the main window was activated which
leads to funny results with external editor windows.

Change-Id: I657ef7e429256f9c098b1fc744d40ffbc2bb5260
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/coreplugin/documentmanager.h

@@ -142,13 +142,15 @@ signals:
     /// emitted if one document changed its name e.g. due to save as
     void documentRenamed(Core::IDocument *document, const QString &from, const QString &to);
 
+protected:
+    bool eventFilter(QObject *obj, QEvent *e);
+
 private slots:
     void documentDestroyed(QObject *obj);
     void fileNameChanged(const QString &oldName, const QString &newName);
     void checkForNewFileName();
     void checkForReload();
     void changedFile(const QString &file);
-    void mainWindowActivated();
     void syncWithEditor(const QList<Core::IContext *> &context);
 };