[syslinux] MEMDISK, MDISKCHK.COM

[Miller, Shao]

hpa: Thanks!  Any chance of the 3.86 branch, too?  I know you'd like to
shift all development, so I'll be using the pathbased tree while
developing.

Gert: I'd like to re-emphasize that _older_versions_of_MEMDISK_ also
suffer for this user.  I'm just throwing that out there to maintain some
distance between "bug" and "new patch."

Now that H. Peter has merged this, it should be easy to produce a
"--no-scan" (or some other name) argument that your user can try.  It
might reveal a problem with probing sequential drive numbers on that
BIOS.

- Shao Miller