ser-unix.c: Add hardware flow control support

[Maciej W. Rozycki]

On Fri, 30 Mar 2007, Daniel Jacobowitz wrote:

> I noticed while looking for the right place to put the option that we
> have an empty "set serial".  Perhaps it should go under that instead.
> No strong preference.

 Well, we have "set remotebaud", which is at the top-level as well.  And 
which actually raises a question as to whether "set remoteflow" should not 
be handled through "struct serial_ops" too?  This way other serial 
interfaces would have a chance to handle the option as well if somebody 
cared.

 Any opinions?

  Maciej