[syslinux] Syslinux 6.04-pre3

[H. Peter Anvin]

As suggested, I have made a 6.04-pre3 release. In addition to updating gnu-efi
to the latest version available (3.0.9 + a few patches) I wanted to make the
tree compile with -Werror on my box, which resulted in pulling a thread which
in turn caused a whole bunch of things to unravel :)

The end result was that I ended up refactoring much of the tree so that it now
avoids building a ton of BIOS-specific files for the EFI platforms. It also
looks like pxelinux pulled in the entire thread library for absolutely no
reason; I have fixed that now.

So way bigger a change set than I wanted for this release, but hey... it
needed to happen I guess.

	-hpa