conflict with the old scheme and cause a "reroll" or "invalid checksums". This
also avoids clobbering the FreeBSD distcache.
Use a revision in the DISTNAME for USE_GITHUB in case we need to bump this
again for anything. It's more a hint of how to handle it in the future.
Reported by: mat
Discused with: mat, antoine, swills
With hat: portmgr