EXPIRATION_DATE format

[Sergey Matveychuk]

Because of EXPIRATION_DATE format is not documented, it deffer from port 
to port:

net/partysip/Makefile:EXPIRATION_DATE=2004-08-20
print/acroread/Makefile:EXPIRATION_DATE=November 21, 2004
www/netscape47-communicator/Makefile:EXPIRATION_DATE=12/07/2004

I think it should be fixed to common YYYY-MM-DD format?

-- 
Sem.