bug#11309: 24.1.50; Case problems with [:upper:] and Cyrillic, Greek

[Mattias Engdegård]

As it turns out I had completely forgotten about Fupcase with a character 
argument -- (upcase ?ß) previously returned ?ß but ?ẞ after the change -- which 
was caught by casefiddle-tests. Now, what to do about it?

One solution would be the previous plan B: set upcase[ß]=nil, modify the 
uppercasep logic, and we will have (upcase ?ß) => ?ß again. However, I would 
argue that the current state is actually preferable:

Upcasing ß to ß never really makes sense. Words containing ß are written with 
SS in upper case: groß -> GROSS - which is one reason why the 
character-to-character use of Fupcase normally cannot be used for text 
containing the letter. The capital ß, ?ẞ, is still not widely employed but one 
of its purposes is when it is important to preserve the exact spelling of 
proper names when written in all caps: Gauß -> GAUẞ, not GAUSS. (I wouldn't be 
surprised if this will eventually become the general convention for all text, 
but we are getting ahead of society here.)

For these reasons, I'm adapting casefiddle-tests and calling it a feature.