This patch reduces roottest/root/io/geom/runreadGeo.C from 50sec to
21sec, by building the list using AddLast() instead of AddAt(i).

Now it spends 1/3 of its time in TObjArray::IndexOf() which is called by

~TGeoBBox -> ~TGeoShape -> TObjArray::Remove, at TGeoShape.cxx:194:

if (gGeoManager) gGeoManager->GetListOfShapes()->Remove(this);


git-svn-id: http://root.cern.ch/svn/root/trunk@19808 27541ba8-7e3a-0410-8455-c3a389f83636