bug#1881: ^M in the info files

[Eli Zaretskii]

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>       FORGED_RCVD_HELO,SPF_SOFTFAIL autolearn=no version=3.1.0
> From: Stefan Monnier <address@hidden>
> Cc: address@hidden,  address@hidden,  address@hidden,  address@hidden
> 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.