scripts: Fix helper edge cases

Propagate patch and module-list failures, normalize the script
directory, and expand the actual Mercurial subrepository name when
matching paths. Keep the existing no-optional-patches behavior
unchanged.

scripts/list-non-source-files

@@ -8,7 +8,7 @@ prefix_matches() {
   f="$1"
   shift
   for s in "$@"; do
-    if [ "$f" = "$s" ] || [ "${f#s/}" != "$f" ]; then
+    if [ "$f" = "$s" ] || [ "${f#"$s/"}" != "$f" ]; then
       return 0
     fi
   done