casa-mp-base

Travis: Prefer public archives over private ones

I had tried to do this with preferred_hosts before, but it appears to
have no effect on archive_site_local.

See: https://trac.macports.org/ticket/57720

Instead list both the public and the private URLs in archive_site_local.
They appear to be tried in the order listed.

But then we need to fix the base bug with multiple URLs in
archive_site_local:

See: https://trac.macports.org/ticket/57718

See: https://trac.macports.org/ticket/54800
See: https://github.com/macports/macports-ports/pull/3099