bad xon/xoff handling by qrlogin

[dlove]

qrlogin doesn't pass C-q, C-s to the remote system. Possible clues from
the Emacs FAQ:

          If your connection to Emacs goes through multiple `tty' and/or
          `pty' devices, they may be using XON/XOFF flow control even
          when it is not necessary.

          Eirik Fuller <eirik@theory.tn.cornell.edu> writes:

               Some versions of `rlogin' (and possibly `telnet') do not
               pass flow control characters to the remote system to
               which they connect.  On such systems, Emacs on the
               remote system cannot disable flow control on the local
               system.  Sometimes `rlogin -8' will avoid this problem.

               One way to cure this is to disable flow control on the
               local host (the one running `rlogin', not the one
               running `rlogind') using the `stty' command, before
               starting the `rlogin' process.  On many systems, `stty
               start u stop u' will do this.

See also #819.