Revisit version compatibility code

[boeckmann]

Currently, FDISK can be made more or less compatible with different DOS / Win9X and FDISK versions through version flags. This code could benefit from a little cleanup. Especially the Win9x and FreeDOS compatibility modes seem a little bit outdated.

There is also a problem with drive letters differing between FDISK and DOS, in cases where FDISK supports file systems not supported by the kernel, or the other way around.

@PerditionC FDISK considers FreeDOS Kernel to be compatible with Win95 feature wise, but not Win98. This may be outdated? I am not aware of any functions regarding partitioning and FAT that Win98 supports, but FreeDOS Kernel does not?

I am thinking of streamlining it like this: FDISK compatibility versions:
Version 7 (Win95), 8 (Win98), 9 (FreeDOS)

With 9 being the default, enabling some new FDISK features:

• LBA_MARKERS (CHS value 1023 instead of wrap-around) = ON
• Logical LBA Partitions inside LBA extended

And DOS / Win9x compatibility <=8:

• LBA_MARKER=OFF, aka CHS cylinder overflow
• NO LBA partitions insidde LBA extended, regardless of end sector (MS-FDISK compatibility!)

To be extended...