Move source files out of the root directory; the root is a mess and
has become virtually unmaintainable.  The Syslinux core now lives in
core/; the Linux and generic utilities has moved into utils/, and
copybs.com has moved into dos/; it had to go somewhere, and it seemed
as good a place as any.

Assemble all files to ELF instead of using the NASM built-in linker.
This can enable us to do actual linking in the future.

Use $(CC) in gcc_ok macro, not plain gcc.  This seems to work, iff the
gcc_ok macro is declared with =, not :=

Some old distros would have <linux/fs.h> poison the namespace with a
non-glibc "struct statfs".  Hack around it.

Verify that we have an ext2 or ext3 filesystem early on.

Conflicts:

	extlinux/extlinux.c

--once now supported for extlinux; some infrastructure for syslinux
there as well, need implementation in all the various installers,
however.