breaks zero-extension of the 16-bit memory size return from the BIOS.
on at least one system, the trash left in the upper half of %eax
causes the kernel to crash during VM system initialization when it
thinks it has on the order of 2**31 bytes of memory to play with.
We now *say* mov %eax,%ebx, but *mean* mov %ax,%bx..
little hacking by me. This isn't strictly identical to his 920312
release -- I've hacked it a bit -- but since we are taking over change
control it doesn't matter much.
is