Merge the SYSLINUX and EXTLINUX patching code and core code, removing
EXTLINUX as a separate derivative.  All the disk-based systems now use
the same code.

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

ROOT_FS_OPS belongs in .rodata, and make it the same format.

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

the extlinux.sys will be installed in btrfs first 64K blank area, and the
extlinux.conf must be in root dir...

Signed-off-by: Alek Du <alek.du@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

FILENAME_MAX was 2^8 in all variants by now; make it a common define.
Libraries mangle/unmangle; we have generic_mangle_name for Unix-like
filesystems, and unmangle now defaults to simple strcpy.

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

Remove the assembly definition of Files in isolinux and pxelinux.
Still to do: remove dependencies on Files living in .bss16 space.

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

Instead of using conditional compilation, just set the root filesystem
type in the assembly stub.

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

ldlinux.asm and extlinux.asm are by now extremely similar.  Merge
them.

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

removes the unused variables in ldlinux.asm

Well, something goes ugly but it works. And I still need spend some more time
to make the code much better.

For now, I added a temporary file load_config.c that would be merged into
extlinux.c file later, which would make my later work be much easier.

And in order to get rid of the conflict noisy message from the open function
in ui.inc and the open function defined in the unistd.h, I changed the
open in core to core_open. It may be ugly, but it works :)