+dit(bf(RSYNC_RSH_IO)) The RSYNC_RSH_IO environment variable allows you to
+override the blocking IO default for the shell specified in RSYNC_RSH. Set
+it to either "blocking" or "non-blocking". This value is only used if the
+remote-shell choice exactly matches the value of the RSYNC_RSH variable.
+Otherwise the default blocking-IO value will be used, as mentioned in
+the --blocking-io option's description above.
+