UNG code contains overrides of default ERP5 UI and KM UI which breaks it so add theme to its default skin selection (same way as KM).

Otherwise other directories may be considered as part of erp5.util
(such as product).

Single quotes need escaping, double don't.

- Handle splitted SM, including those at root.
- Allow caller to drop root SM (via 'get_matching_key').
- Fix detection of draft trees that are out of sync
  (cf commit 200bf7cb)