Draft: os: Lock file: No link phase, never unlink foreign lock, hardening of abnormal situations
MR for issue #1138.
1st commit is unrelated and for issue #1131 (MR !611 (merged)), which should be merged before.
MR for issue #1138.
1st commit is unrelated and for issue #1131 (MR !611 (merged)), which should be merged before.