Close variable chooser on escape (if it has focus).

Task-number: QTCREATORBUG-4307

Change-Id: Ib85f5fda1310fe6fb0e0824488fb6c79962ae35b
Reviewed-on: http://codereview.qt.nokia.com/624
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Robert Löhning <robert.loehning@nokia.com>

src/plugins/coreplugin/variablechooser.h

@@ -58,6 +58,9 @@ public:
     explicit VariableChooser(QWidget *parent = 0);
     ~VariableChooser();
 
+protected:
+    void keyPressEvent(QKeyEvent *ke);
+
 private slots:
     void updateDescription(const QString &variable);
     void updateCurrentEditor(QWidget *old, QWidget *widget);