New CIDR type and fixed INET type, from D'Arcy.

src/backend/utils/adt/inet.c

src/include/catalog/pg_opclass.h

src/include/catalog/pg_operator.h

src/include/catalog/pg_proc.h

src/include/catalog/pg_type.h

src/include/utils/builtins.h

src/include/utils/inet.h