[Bug: 21.5-b28] Control-1 chars are second-class citizens in regexp ranges

[Aidan Kehoe]

21.4 doesn’t have the problem; it found its way in between the releases of
21.5.18 and 21.5.19, which from the mentions of regex.c in src/ChangeLog
implicates Ben. Nothing obvious strikes me from eyeballing the diff between
the two, so it may be another file.

 Ar an seachtú lá de mí Feabhra, scríobh Aidan Kehoe: 

 > [...]

-- 
¿Dónde estará ahora mi sobrino Yoghurtu Nghe, que tuvo que huir
precipitadamente de la aldea por culpa de la escasez de rinocerontes?