Log Message:
the scripts.sil.org site is using ViewVC to dynamically generate a
new .tar.gz for each download.   each new .tar.gz has a new gzip
timestamp, so the gz is different each download (the tar itself is
the same).  this makes it impossible to match the checksum in distinfo,
so we pull it from a static file on MASTER_SITE_BACKUP instead,
as suggested by Thomas Klausner.