Do not use QAbstractItemModel::reset().

Change-Id: Ie49bdf576a6d3543aef6df133b27c8827775c935
Rationale:
    a) It is conceptually cleaner to do the changes to the model
       in between calls to beginResetModel() and endResetModel,
       respectively.
    b) The function is deprecated in Qt 5, for exactly that reason.
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/debugger/stackhandler.h

@@ -94,7 +94,7 @@ private:
     QVariant data(const QModelIndex &index, int role) const;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const;
     Qt::ItemFlags flags(const QModelIndex &index) const;
-    Q_SLOT void resetModel() { reset(); }
+    Q_SLOT void resetModel() { beginResetModel(); endResetModel(); }
 
     StackFrames m_stackFrames;
     int m_currentIndex;