[syslinux] "NOESCAPE 1" is easily escapable

[Paul Whittaker]

(I apologise if this has already been reported - the archive isn't very 
searchable.)

At present the NOESCAPE keyword seems rather useless, because a boot 
prompt is offered whenever attempts to load a boot image is interrupted 
using <Ctrl>C.  Intuitively, I would expect "NOESCAPE 1" to lock this 
down also, and that {sys,pxe,iso.ext}linux would simply fall through to 
the impicit or explicit ONERROR behaviour.  It doesn't.

This is particularly a problem for those using the password protection 
features of menu.c32, because access to a boot prompt will completely 
subvert this protection.  For example, if I have a standard boot image 
and a password-protected privileged boot image, I can start booting the 
standard image, interrupt the boot, and then enter the name of the 
privileged image to boot it *without entering the password*.

P.S. I've also noted that use of "IMPLICIT 0" can have some rather 
unexpected side-effects when using menu.c32.  Adding a warning about 
this to README.menu might be a good idea.