are no longer limited to a virtual address space of 16 megabytes,
only mask high two bits of a virtual address. This allows to load
larger kernels (up to 1 gigabyte). Not masking addresses at all
was a bad idea on machines with less than >3G of memory -- kernels
are linked at 0xc0xxxxxx, and that would attempt to load a kernel
at above 3G. By masking only two highest bits we stay within the
safe limits while still allowing to boot larger kernels.
(This is a safer reimplmentation of sys/boot/i386/boot2/boot.2.c
rev. 1.71.)
Prodded by: jhb
Tested by: nyan (pc98)
f0e19d90c0