bug#4047: 23.1.1: hexl-mode doesn't like UTF8 files with a byte-order mark

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 08 Aug 2009 15:20:10 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 4047@emacsbugs.donarmstrong.com
> 
> The cause of the problem is this: [...]

I probably should have said explicitly that the end result of all I
described is that the "-hex" command-line argument to `hexl' is
encoded by utf-8-with-signature, and becomes "\357\273\277-hex",
which, of course, utterly confuses `hexl'.

Btw, I doubt that any encoding that uses BOM can ever be appropriate
for encoding command-line arguments.  Maybe we should treat them
specially in call-process and its ilk.