lang/algol68g: unscheduled update of the port to version 3.5.7
This was urged because of the little time between the last two
releases and Marcel's disgusting habit of removing old tarballs
upon every new release, so the distfile for version 3.5.6 have
not been cached on our servers. Add fallback download location
to prevent this happening again.
Reported by: cy, pkg-fallout, Mamoru IWAKI