Arch users: update pacman soon

The Arch Linux developers recently released version 5.0 of the pacmanpackage manager with some useful new features: "The release ofpacman-5.0 brought support for transactional hooks. These will allow us to(e.g.) run font cache updates a single time during an update rather thanafter each font package installation. This will both speed up the updateprocess, but also reduce packaging burden for the Developers and TrustedUsers." Unfortunately, once they start using these hooks, olderversions of pacman will no longer understand the resulting packages. Thatwill happen on April 23, so all Arch users need to have upgraded bythen.