the flag, fall back to the old INT13/AH=02 function if that fails.
This way of operation is less likely to fail with modern BIOSes and
large disks of strange geometries.
PR: i386/70241
Submitted by: Valentin Nechayev <netch <@> netch.kiev.ua> (inital version)
Discussed with: jhb (by Valentin Nechayev)
Tested on: bochs (with EDD turned on or off by patching the BIOS), PCs