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/libs/cplusplus/OverviewModel.cpp

@@ -239,6 +239,7 @@ Symbol *OverviewModel::symbolFromIndex(const QModelIndex &index) const
 
 void OverviewModel::rebuild(Document::Ptr doc)
 {
+    beginResetModel();
     _cppDocument = doc;
-    reset();
+    endResetModel();
 }