tty structures, and on some machines (namely the DraCo internal lpt, and some
multi-i/o boards for Amigas and DraCos), tying spltty to the pretty high printer
interupt level would hurt serial performance.
On all affected ports but Amiga, spllpt() has been defined in machine/intr.h
to be spltty(), thus preserving old behaviour. Portmasters are encouraged to
change is, if they feel something else is better (e.g., one of its own were
possible).
