executing any image, not just a script.  (This will enable pxelinux to
use relative URIs, should it wish to.)

Print error status using strerror().

allows us to avoid execution loops without having to hack around the
image registration order.

Add scripts as an image format (since it's trivial to do).

userptr_add().

refer to them by name from the command line, or build them into a
multiboot module list.

Use setting image->type to disambiguate between "not my image" and "bad
image"; this avoids relying on specific values of the error code.

standard and so don't belong in include/elf.h

generic ELF loader, to be used by the multiboot code.

and get_memmap() in image/segment.c