swap on sd0b and sd1b and sd2b
   configures for swap on sd0b, sd0j, and sd1b.

This is an artifact of config.new(8) not dealing nicely with differing
values of MAXPARTITIONS, and instead always assuming that disk minor
numbers are (unit * 8 + partition).  Currently it affects the Amiga
port.  Someone should fix it.

Note that simply using MAXPARTITIONS throughout the source is *not*
correct; you're supposed to be able to configure a kernel for any
architecture from a system running on any other architecture.  This
would mean that either MAXPARTITIONS must be consistent across
architectures, or config.new(8) needs to generate specifications that
explicitly calculate the `unit * MAXPARTITIONS + partition' at compile
time.