Drag onto athlete tab to switch tabs

.. this allows us to drag and drop between athletes or
   to switch athlete if dropping from outside of GC.

.. also added context to the mime data so the compare pane
   will know where the dragged object has come from (ie. it
   may be from a different athlete).

src/IntervalTreeView.cpp

@@ -65,6 +65,7 @@ IntervalTreeView::mimeData (const QList<QTreeWidgetItem *> items) const
     stream.setVersion(QDataStream::Qt_4_6);
 
     // pack data 
+    stream << (quint64)(context); // where did this come from?
     stream << items.count();
     foreach (QTreeWidgetItem *p, items) {
 
@@ -73,7 +74,7 @@ IntervalTreeView::mimeData (const QList<QTreeWidgetItem *> items) const
 
         // serialize
         stream << p->text(0); // name
-        stream << static_cast<const void*>(i->ride);
+        stream << (quint64)(i->ride);
         stream << i->start << i->stop; // start and stop in secs
         stream << i->startKM << i->stopKM; // start and stop km
         stream << i->displaySequence;