Do not clear the IXON flag in termios.c_iflag.
Bug 54 did not actually ask for this flag to be kept,
but the cable I am using doesn't seem to have the handshake
lines connected right, so XON/XOFF is a must at 38400 bps,
at least until ELinks learns to send padding based on terminfo.
Any user who has bound actions to Ctrl+S or Ctrl+Q and finds that
they no longer work should just "stty -ixon" before running ELinks.
We don't have any default bindings for those keys, fortunately.