make a clone of this header list. This supercedes the parent
function of the same signature.
ViaList vlist = new ViaList();
for (int i = 0; i < this.sipHeaderVector.size(); i++) {
ViaHeader v = (ViaHeader)
((ViaHeader) (this.sipHeaderVector.elementAt(i))).clone();
vlist.add(v);
}
return (Object) vlist;