`"$SHELL" -c "printf %s \$KSH_VERSION"` as part of the shell version
detection for ksh and mksh was expanding to `printf %s $KSH_VERSION`
inside of shell. This resulted in `$KSH_VERSION` being substituted as
multiple arguments to printf. While (afaik) unspecified, mksh, bash
and zsh resort to repeating the format strings. This resulted in all
spaces missing from `$shell`, which in turn caused the string cleanup
to fail: `Shell: mksh @MIRBSDKSHR562017/08/29`
Quoting `$KSH_VERSION` causes it to be given to printf as a single
argument, which preserves its spaces. The output after this change
looks like follows: `Shell: mksh R56 2017/08/29`
