Editor: Fix resizing of proposal widged

Stop resizing width on scrolling the proposal
widget via drag of the scrollbar.

Task-number: QTCREATORBUG-7925
Change-Id: I948a0ec1bba8a9294b8a65b5eaa72063bbede48f
Reviewed-by: Christian Stenger <christian.stenger@digia.com>

src/plugins/texteditor/codeassist/genericproposalwidget.h

@@ -65,6 +65,8 @@ private:
 
 private slots:
     void updatePositionAndSize();
+    void turnOffAutoWidth();
+    void turnOnAutoWidth();
 
 protected:
     virtual bool eventFilter(QObject *o, QEvent *e);