This fixes tags like 'xfce4-dev-tools-4.20.0'. * tests/import-git.scm ("latest-git-tag-version: prefix contains pre-release words"): New test. * guix/import/git.scm (latest-tag): Don't filter out pre-releases tags. (version-mapping): Filter out pre-releases tags from versions. * gnu/packages/xfce.scm (garcon, thunar-archive-plugin, xfce4-dev-tools): Remove FIXME comments for the 'generic-git' updater. Change-Id: I7683200fa451d7fad153aa08fa9d5761688de01d