rsync turns on blocking I/O mode if remote shell command is rsh
(ie. matched RSYNC_RSH) to work around some broken rsh implementations
on other platforms.
The submitter of the rsh->ssh patches overloaded RSYNC_RSH for ssh.
That turns out to be a Wrong Thing. This change implements the parallel
RSYNC_SSH.
PR: 26376
Submitted by: adrian
