Some tools might assume that the reloc offset being 64 automatically
means it's really a Windows file.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Explicitly add the pointer to the PE header in the binary.  That way
we might be eventually able to create a merged DOS/Win32 binary.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Additional fixes for the 32K limits in the installers.  In the case
of the DOS installer, that means changing it from COM format to EXE
format (since COM format has a 63K hard limit); retain the name
syslinux.com for user compatibility, though (DOS doesn't care what the
extension except for pathname search; if it finds an MZ EXE header it
will use it.)

With the change to EXE means having to handle more than one segment.
Since we don't have a real DOS compiler we have to wing it a bit.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>