use the `a_entry' field from the kernel's header as a base.
Pass on a new DDB magic number to the kernel, so kernels linked for a
different KERNBASE value can apply a correction when booted from old
bootblocks.
ports' boot programs. Also added support for loading gzip'd kernels,
useful for booting from floppy. From Jason R. Thorpe <thorpej@nas.nasa.gov>,
tested by Matthew Green <mrg@eterna.com.au> and Erik Fair <fair@clock.org>.