There are new country codes RS for Serbia and ME for Montenegro.
http://www.iso.org/iso/en/prods-services/iso3166ma/03updates-on-iso-3166/nlv12-div.htm
I would suggest the following changes:
In zone.tab
Change the line:
CS +4450+02030 Europe/Belgrade
to:
RS +4450+02030 Europe/Belgrade
Add:
ME +4247+01928 Europe/Podgorica
In europe
Add:
Link Europe/Belgrade Europe/Podgorica
Mark