Use "-nostdinc -iwithprefix include" to prevent the inclusion of
system header files, but still permitting *compiler* header files.

Break off execute() into its own source file, with the intent of being
able to re-use it for a CLI module.

H. Peter Anvin wrote:
> Erwan: I would have to get you to do this, since it would mean
> changing the license (trying to keep libcom32 under the BSD/MIT
> licenses), and you have them under your own copyright (as opposed to
> mine), which means I can't do this change.

Please find attached the patch to changing the license to MIT on modules
I did contribute in com32/modules/.

Allow MENU EXIT to "exit" to an arbitrary menu.  This is really just a
variant of "MENU GOTO", but it allows displaying an exit marker.

Two bugs:

- We didn't strip ^ symbols inheriting from MENU LABEL to MENU TITLE
- We did consider_for_hotkey() with the wrong menu (the submenu
  itself, as opposed to the parent menu.)

As part of these changes, make a function available to create an
uninitialized, mutable refstring (that can be constructed and then
used as a refstring, that is.)

When we realloc() a block larger, try to protect the free block
following it from being immediately allocated by something else by
placing it at the end of the freelist instead of the beginning.

Change the realloc() implementation to allow in-place growth.  This is
an important step in handling files without knowing their sizes a
priori.

Correctly make it so MENU TITLE can be inherited upward as MENU TITLE
unless one is provided.

Color directives would always end up attached to the root menu, no
matter what menu declaration they where actually located in.