[syslinux] SYSLINUX 2.20-pre9 released, now with EXTLINUX

[H. Peter Anvin]

... and this is pretty much the first version of 2.20 which can be 
considered likely to actually work, except for the Win32 installer.

The big news in this prerelease, by far, is EXTLINUX.

I'm also hacking on a "simple menu system" as a com32 module; basically 
a hack to re-parse the config file and display a menu of its label 
statements.  Don't know when that'll be ready yet, though.

Please test it out and let me know what's broken.

Changes in 2.20 (so far):
         * SYSLINUX: Support FAT32 and EDD.  As an unfortunate
           consequence, LDLINUX.SYS is no longer an ordinary file; it
           is block-mapped at install time, which means it can only be
           written using the syslinux installers.
         * SYSLINUX: Reorganize the source code for the installers;
           each one of the installers (dos, win32, unix, mtools) is now
           built in its own subdirectory.  In particular, "mtools" is
           the unprivileged installer which uses mtools; "unix" is the
           privileged installer which uses system calls.
         * ALL: "label" statement information is now stored in a
           compressed format, which means that a lot more labels are
           permitted (500-1000 in a typical configuration, but depends
           on the complexity.)
         * EXTLINUX: New derivative, which boots from an ext2/ext3
           filesystem.
         * SYSLINUX: The DOS installer can now optionally write the
           boot sector to a file instead of the real boot sector.  This
           is currently not supported in any of the other installers,
           but should be added to the Win32 installer at some point.