sbbs

As noticed while trouble-shooting issue #813, calling comOpen() would
(on Linux, at least) set the port baud rate to 0 bps (B0) which in
most or all Linux serial drivers triggers special logic to deassert DTR and
RTS signals (to the modem, to attempt to "hangup" any connection).

If the app (e.g. sexpots) did not explictily set the port baud rate after
calling comOpen(), the port would be unusable. This is not how comOpen() works
on Windows.

So rather than just overwrite all the bits in termios.c_cflag, we clear the
fields we know we want to, set the bits we want, and leave the rest (which
usually includes the current baud rate, if CBAUD is defined) as-is.