in borg 1.x, we used to put a timestamp into the archive name to make
it unique, because borg1 required that.
borg2 does not require unique archive names, but it encourages you
to even use an identical archive name within the same SERIES of archives.
that makes matching (e.g. for prune, but also at other places) much
simpler and borg KNOWS which archives belong to the same series.
at some places, the docs were not updated yet.
for borg 1.x, -a (aka --glob-archives) expected
sh: style glob patterns ONLY (but one must not
give sh: explicitly).
for borg 2, -a (aka --match-archives) defaults
to id: style (identical match), so one must give
sh: if one wants shell-style globbing.
