Variable manager uses "update request" mechanism.

For now that removes the CURRENT_DOCUMENT variable and derivates.

src/plugins/qt4projectmanager/qt4projectmanager.h

@@ -107,6 +107,7 @@ private slots:
     void editorAboutToClose(Core::IEditor *editor);
     void uiEditorContentsChanged();
     void editorChanged(Core::IEditor*);
+    void updateVariable(const QString &variable);
 
 private:
     QList<Qt4Project *> m_projects;