bug#1881: ^M in the info files

[Eli Zaretskii]

> X-Spam-Status: No, score=-1.2 required=5.0 tests=AWL,BAYES_00,
>       FORGED_RCVD_HELO,SPF_SOFTFAIL autolearn=no version=3.1.0
> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: 876-done@emacsbugs.donarmstrong.com,  emacs-pretest-bug@gnu.org,  
> bug-gnu-emacs@gnu.org,  emacs-devel@gnu.org
> Date: Mon, 12 Jan 2009 15:54:38 -0500
> 
> Hmm...curious, why does it involve coding priorities?

You suggested to introduce a way of controlling which possible
encodings will _not_ be acceptable by the caller of
detect-coding-region/string.  These primitives work by scanning the
coding_priorities[] array and checking them against those categories
that has been rejected based on the text in the region/string.  See
detect_coding and detect_coding_system.