We keep a scope list that is checked to verify that we do not try
to dump duplicate scopes or variables. Since the scan_item routine
can not add duplicate scopes we only need to sort the list after
the scan_item routine is called. Calling it every time a scope
was added was creating a significant startup delay for gate level
simulations since the sort routine is called for every scope in
the design (possibly thousands of times).
This mostly matches what was done for the LXT dumper except the
LXT dumper was incorrectly sorting before not after scan_item
was called. This would not catch a duplicate variable just
after a scope was added in a $dumpvars call.