Releasing 2.4.2

[Rainer Müller]

MacPorts 2.4.2 is now out and should be available via selfupdate over
rsync shortly.

Ryan, could you please mirror the tarballs and signatures from the
GitHub release to distfiles.macports.org?

https://github.com/macports/macports-base/releases/tag/v2.4.2

I will hold back updating the website and official announce mail until
we have new .pkg installers to avoid breaking the download links. At the
moment, users can still install MacPorts 2.4.1 which will then
automatically update itself to version 2.4.2.

Rainer