bug#13041: 24.2; diacritic-fold-search

[Drew Adams]

> Perhaps the name/description should speak in terms of Unicode 
> char compatibility or equivalence.  Perhaps a name like
> `string-less-compat-p'?  Or `Unicode-equivalent-p'?  Or
> `string-equivalent-p'?

In the last two suggestions I forgot about the "less" part.

Taking a quick look at the Unicode specs, it seems that what we do involves
(Unicode) "compatibility equivalence".  But it also seemed that Eli was saying
that for us this is not distinguished from (Unicode) "canonical equivalence".

So perhaps `unicode-equivalence-less-p'?  Or if there is a risk of confusion
with char (not string) comparison, then perhaps `unicode-equiv-string-less-p'?
Or just `equiv-string-less-p'?