bug#16731: 24.3.50; Latin small letter sharp s is not considered lower-case

[Stefan Monnier]

> How will we then be able to distinguish between lower-case characters
> that have no upcase variant and characters that are not lower-case
> characters at all?

Right: to handle this, we need to distinguish characters that are
lower-case without an uppercase variant from characters which are
neither lowercase nor uppercase.

We could do that by saying that the upcase table should return nil or -1
for ß, to indicate that the upcase version is "missing".  But such
a change will probably require carefully revising "all" the code that
uses those tables.


        Stefan