In require: - Adjust Loader.clone() to use a singleton per path/source - Add Loader.default for the initial instance - Add Loader.using for temporary replacement - Adjust Loader.use() to use a callback to control loader scope. - Replace Loader.current with more dynamic context. - Remove Script instance ownership wrangling    * Replaced by Loader context, and current Script's Loader changes - Remove Loader id requirement from Script id references    * Except in allowed[], to prevent cross Loader confusion
In require:
- Adjust Loader.clone() to use a singleton per path/source
- Add Loader.default for the initial instance
- Add Loader.using for temporary replacement
- Adjust Loader.use() to use a callback to control loader scope.
- Replace Loader.current with more dynamic context.
- Remove Script instance ownership wrangling
   * Replaced by Loader context, and current Script's Loader changes
- Remove Loader id requirement from Script id references
   * Except in allowed[], to prevent cross Loader confusion

jka6502/stratum,jka6502/stratum