* CORE_identifier:
  - Enforce stronger invariant of path representation.
  - Handle better absolute vs relative path distinction.
COMMON_process.pread_lines: Wrap it too.
* CORE_config.ressource_root: Make it absolute.
* CORE_vfs.owner: New operation.
* COMMON_unix: New. (Was missing for a long time, too lazy to rewrite the history.)