(65536 * 32 - 1), but MAKEDEV only supports up to (32 * 32 -1). Device
names use the unit number in base 32 for all "digits".
This required fixing an old bug in MAKEDEV:ttyminor(). Its arg was the
global $unit instead of $1.
Reminded by: Valentin K. Ponomarenko <valka@krog.ukrtel.net>
MFC-after: 1 week