[patch] Forbid run with a core file loaded

[Eli Zaretskii]

> Date: Sun, 6 Jun 2010 21:50:34 +0200
> From: Jan Kratochvil <jan.kratochvil@redhat.com>
> Cc: mark.kettenis@xs4all.nl, brobecker@adacore.com, gdb-patches@sourceware.org
> 
> No regressions on {x86_64,x86_64-m32,i686}-fedora13-linux-gnu.
> 
> OK to check-in?

The part for the manual is okay with me.  Thanks.