* Use refs/dgit-fetch/DISTRO rather than refs/dgit-fetch/DISTRO,
which leads to less duplication and so less clutter.
* Enforce a reasonable syntax for nominal distro names.
* Use refs/dgit-fetch/DISTRO rather than refs/dgit-fetch/DISTRO,
which leads to less duplication and so less clutter.
* Enforce a reasonable syntax for nominal distro names.