mksh: 51 -> 52

‘This release has a nonzero chance to break existing scripts that
use some extension features – I had to quote some tildes in
dot.mkshrc and a variable expansion in ${x/y"$z"} in MirWebseite
(the $z) – twice!. As usual, test!’

-- https://www.mirbsd.org/permalinks/news_e20151212-tg.htm