bug#20316: 24.5; `string-lessp' doesn't respect value of LC_COLLATE

[Eli Zaretskii <eliz@gnu.org>]

> From: Alexis <flexibeast@gmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>, michael.albinus@gmx.de
> Date: Tue, 14 Apr 2015 10:55:53 +1000
> 
>     So by default, Emacs sorts disregarding locale-specific ordering, basically using the Unicode codepoints of the characters to order them. 
> 
> This makes sense given what you've said above, but can this still be referred to as 'lexicographic' ordering? To me, 'lexicographic ordering' is ordering as per a dictionary for the relevant language, not by codepoint for an arbitrary encoding. Is this wrong?

I think we use "lexicographic" for lack of a more accurate word.  We
could use something like "code point (binary) order", but would that
be clear enough to be useful?

Note that we are not alone in this; at least this page:

  http://en.cppreference.com/w/cpp/string/byte/strcoll

says that the C function 'strcmp' does a "lexicographical comparison".
So do a few other similar pages; google for "difference between strcmp
and strcoll".

> One of the package's users had imported a set of contacts, then expected to be able to sort those contacts according to Croatian rules, using `org-sort' (from `org.el'). However, to quote the user, this resulted in the contacts being sorted according to the English alphabet rules where the contact entries which start with Croatian characters (Č,Ć,Đ,Š,Ž) are at the end of the list, iow. after 'Z' entries, although it should go like this:
> 
> A,B,C,Č,Ć,D,Dž,Đ,..S,Š,..Z,Ž

That's "collation order" in action, note that the diacritic order is
applied _after_ the alphabetic order of the base characters.  That's
what string-collate-lessp does.