Improve subcommand listing for help string

src/bin/saturnin.skel

     echo ""
     echo "valid sub-commands:"
     echo ""
-    ls "$SATURNIN_LIBEXEC" \
-      | sed -e 's/saturnin-/    /'
+    find "$SATURNIN_LIBEXEC" \
+        -mindepth 1 \
+        -maxdepth 1 \
+        -executable \
+      | sed -e 's/.*saturnin-/    /' \
+      | sort
+    return "$FFOO_EXIT_OK"
 }
 
 version_info() {