PSREPLACE: include control characters in detection test
PSREPLACE: include control characters in detection test

On mksh <= R51, replacing control characters with ${var/x/y}
(PSREPLACE) substitutions is broken -- at least $CCa (\7) fails to
be replaced. In 0.16 this caused regression test failures for
shellquote(). On the master branch, these mksh versions already
refuse to initialise due to other bugs now considered fatal, but
it's still a good idea to robustify the detection test.

lib/modernish/cap/PSREPLACE.t:
- Include $CCa in the detection test so the feature isn't detected
  and used if broken.
- While we're at it, include $CC01 and $CC7F which have often
  caused problems on various bash versions...

modernish/modernish