for get_diskinfo(), whose BIOS call sets %es:%edi in some cases, although
most documentation says that it doesn't change %edi in the cases that
happened to matter (for hard disks).
This shall be in 2.1.6 and 2.2.
Submitted by: Tor.Egge@idt.ntnu.no
(except I kept the unnecessary preservation of %edx and %ecx)