[Xastir] iBook USB to MacBook Pro USB

[Jason KG4WSV]

I've been talking to Keith offline, and I think this was the clue that
got him going:

the Keyspan device special file contains data on the adapter's
location in the USB "tree", so this name will change if it's plugged
in to a different port.  The "191" part of "USA19H191P1.1" will
change.  I've also had it change just by rebooting the computer
(although a power cycle was consistent).

On mac os X every driver I've seen so far (FTDI, keyspan, SI labs, and
I think prolific) uses /dev/tty. and /dev/cu. prefixes, so "ls
/dev/tty.*" will get you zeroed in pretty quickly.

-Jason
kg4wsv