[syslinux] menu shiftkey directive

[Ady]

Hello Peter,

After some tests with MENU SHIFTKEY with different versions of 
Syslinux, I came to the conclusion that, at least for now, it would 
be better to undo commit:
 
<http://git.zytor.com/?p=syslinux/syslinux.git;a=commit;h=7e7139788c8a
c6ffbf474976ad4d1727e0677b9f> 

 "ldlinux: Allow a held shift key to override UI as well as DEFAULT" 
committed on Thu, 22 May 2014.

Although the aforementioned commit makes the current 6.03 branch 
behave as version 4.xx, my tests show that the behavior is 
effectively inadequate and inconsistent.

Although I had been previously nagging you in irc about maintaining 
backward compatibility of the "force-prompt" keys, I have to ask you 
to undo the aforementioned commit before the final release of 6.03 
stable. The behavior of Syslinux 6.03 without this particular commit 
will slightly "break" with the prior "force-prompt" behavior as seen 
in 4.xx when using [vesa]menu.c32, but it will be more consistent and 
clean.

Without this commit, the user can still avoid the automatic launch of 
the default label by the same means (the "escape" "shift" keys), 
which is the most important characteristic of MENU SHIFTKEY.

Please consider this request before the release of 6.03 stable.

TIA,
Ady.