Maven seems to have improved their download management and instead of
having their webpage choose a host they now have a CDN domain.
apache.cs.utah.edu is slow and is failing to finish the downloading.
Re-sort packages, now that the tabs aren't skewing the sorting.
I'm quite confident I had fixed this already, but I had multiple copies
of this file on multiple machines and must have fixed the wrong copy.
CentOS 6 is dead and no longer has update servers. CentOS 7 is older
than Debian 9 (oldstable), so binaries hopefully work on both. More
testing is necessary, but everything's broken now, so this is better
than nothing.
We stop using protoc-artifacts because now the container is
straight-forward enough that we can just use our own. Previously the
"devtoolset" stuff made us want to share the container.
Eric Anderson