Changes taken from the i386 MAKEDEV. Note that the unusual use of 'dd'
to index an array was chosen because 'dd' is on all ports' install media.
This form of this change comes from Andrew Brown; the original idea to
bump the number of ptys this way comes from Brian Marcotte at Panix.
at the end, and as wscons (actually ttyE0) is required to login on the console,
it is probably better that an out of space MAKEDEV fail on some other device.
