Comment 3 for bug 882261

 * Provide a new API for dealing with possible additional unexpected errnos
   while trying to read the lock file. These can happen in some NFS
   environments. If you want to retry the read, set the lock file's
   `retry_errnos` property to a sequence of errnos. If one of those errnos
   occurs, the read is unconditionally (and infinitely) retried.
   `retry_errnos` is a property which must be set to a sequence; it has a
   getter and a deleter too. (LP: #882261)