post-unlock — Notification of a successful path unlock.
The post-unlock hook runs after one
          or more paths have been unlocked.  It is typically used to
          send email notification of the unlock event.
If the post-unlock hook returns a
          nonzero exit status, the unlock will
          not be aborted since it has already
          completed.  However, anything that the hook printed
          to stderr will be marshalled back to the
          client, making it easier to diagnose hook failures.