Expose cleaninput() for use in addons.

Despite its hard-coded use of $input, this can be useful in addons, too.
(I, for example, use this in a "todo.sh subst" addon that delegates to the "todo.sh replace" action after performing a sed-style replacement on the passed pattern and replacement.)

todo.sh

@@ -751,7 +751,7 @@ _list() {
     fi
 }
 
-export -f _list die
+export -f cleaninput _list die
 
 # == HANDLE ACTION ==
 action=$( printf "%s\n" "$ACTION" | tr 'A-Z' 'a-z' )