todo

A real-time serial port device driver, works with RT-Linux and RTAI.

- /dev/ttySn should correspond not to the n'th entry in the table, but to the
  n'th real serial port. We can implement rt_com_setserial that would set
  parameters. Or we can use module parameters:
    insmod rt_com com1=0x2f8,4
  Only those ports listed on the command line would be requested.
  (To my mind both have to be done, but the module parameter stuff should be
  implemented right away, while rt_com_setserial can be done later - Jochen.)

- POSIX tcgetattr/tcsetattr (non-canonical mode only).