Change the command line limit to 2047 characters, which is also the
current kernel limit.  As a result, shuffle around the memory layout
to make the larger buffers fit.

TODO: consider moving vgafontbuf to getcseg, and try to make do with
fewer command line-sized buffers.

Remove the last few uses of getcbuf (to extend trackbuf for shuffle
descriptors, and for temp storage during pxelinux config file search.)
As a result, change the way RBFG_brainfuck is handled in pxelinux (at
some point it's probably not worth maintaining anymore, as RBFG is no
longer widely used); add a .bss2 section for the region between the
RBFG zone and the stack.

Conflicts:

	extlinux/extlinux.c

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

Initial support for the auxillary data vector, a storage mechanism
intended to support boot-once and similar features.

Create a guard section .uibss that explicitly is covering the
potential partial-sector-clobber zone, and contains items which are
safe to assume will only be used after full image load.

Update the memory layout specification.  Remove NASM 0.98.38 bug
workarounds, rebalance the bss sections, and introduce the new section
.adv which contain the auxilliary data vector.

Provide a method for re-loading shuffle descriptors from a buffer in
high memory when the shuffle descriptors are too many to fit in the
buffer.  This can happen when trying to stitch an initramfs together
from parts.  Still need library support for this, however.