Debugger: Clear undo/redo stacks when debugging session is finished

Task-number: QTCREATORBUG-7645
Change-Id: I17df03c5765129c21f38df19ea90c04e937a7217
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/debugger/logwindow.h

@@ -61,6 +61,8 @@ public:
     QString combinedContents() const;
     QString inputContents() const;
 
+    void clearUndoRedoStacks();
+
     static QString logTimeStamp();
 
     static bool writeLogContents(const QPlainTextEdit *editor, QWidget *parent = 0);