HEADS-UP: distfiles have been cleansed

If you work on -current, please make sure you have the current
infrastructure and to read bsd.port.mk(5) and friends.

Specifically:
MASTER_SITES0..9 is dead
prefer
DISTFILES.sufx
to refer to
SITES.sufx

Also: MASTER_SITES* is dead. We decided to replace it with the
much shorter (with no loss of meaning) SITES*

The tree has been entirely converted, and the compatibility glue has
been removed: new stuff must use the new mechanisms.