Suppress the Ctrl+B banner and zero out the timeout.  It's not very
useful for an integrated product, and very visually annoying on NBP
chainload.

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

Add MENU CLEAR to clear the screen on menu exit.

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

Clear away the countdown message before actually running the final
boot.

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

Use the new "exit hook" functionality in gPXE to allow NBP
chainloading from gpxelinux.0.

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

Using the PXE-provided stack complicates things tremendously for gPXE
chainloading support, plus we are hostages to the stack size set up by
the PXE stack (1.5K by spec.)

Use a private stack instead, as the fsc branch already does.

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

gPXE 1.0.0 has support for using the cached DHCP packet from the
previous PXE stack, so do that rather than doing another DHCP.

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

It is often fine to have a sparse file for the output image, so add an
-s option to generate a sparse image.

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

If we see the "quiet" flag for the Linux kernel, also suppress the
early Linux kernel messages; for people who want a completely clean
boot.

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