small changes in the GDML processor (to avoid crashes with elemenent...
small changes in the GDML processor (to avoid crashes with elemenent fractions) and in the GeoModelXML (to add a set element as used in the muons)
small changes in the GDML processor (to avoid crashes with elemenent fractions) and in the GeoModelXML (to add a set element as used in the muons)