* Use zlib's "fossil" site for old tarballs
Following citibeth's suggestion in #2732, use zlib's "fossil"
site (not to be confused with the sqlite team's VCS...) for retrieving
old tarballs.
Digests for 1.2.{8,10} match and both install for me on CentOS 7.
* Use zlib's "fossil" URL as the one true URL
Everything seems to be available at zlib's "fossil" URL, so just use
it as the one and only url.
(and fix a flake8 complaint about a comment)
4e653254c5