Refactor the {load,exec} image operations as {probe,exec}.  This makes
the probe mechanism cleaner, eliminates some forward declarations,
avoids holding magic state in image->priv, eliminates the possibility
of screwing up between the "load" and "exec" stages, and makes the
documentation simpler since the concept of "loading" (as distinct from
"executing") no longer needs to be explained.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Allow the monojob controlling the download to complete before calling
register_image() and friends.  This allows the trailing "ok" from
monojob.c to be printed before the image starts executing (and
possibly printing output of its own).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

For performing installations direct to a SAN target, it can be very
useful to hook a SAN disk and then proceed to perform a filename boot.
For example, the user may wish to hook the (empty) SAN installation
disk and then boot into the OS installer via TFTP.  This provides an
alternative mechanism to using "keep-san" and relying on the BIOS to
fall through to boot from the installation media, which is unreliable
on many BIOSes.

When a root-path is specified in addition to a boot filename, attempt
to hook the root-path as a SAN disk before booting from the specified
filename.  Since the root-path may be used for non-SAN purposes
(e.g. an NFS root mount point), ignore the root-path if it contains a
URI scheme that we do not support.

Originally-implemented-by: Jarrod Johnson <jarrod.b.johnson@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Some shuffling around of the image management code; this needs tidying up.

"kernel".