Don't (mis)use tr/// to remove non-printables

Turns out tr/// *does not support POSIX classes* at all.  This command
could not have ever worked.  (schroedinbug).

src/include-sh/coerce.sh

@@ -27,7 +27,7 @@ coerce__noctl() {
     #
     # Remove non-printable characters
     #
-    perl -CS -Mutf8 -pe 'tr|[:graph:]\n\t ||c;'
+    perl -CS -Mutf8 -pe "s|[^[:graph:] \t\n]||g"
 }
 
 coerce__nofdraw() {