bug#10118: C-w folds case too eagerly

[Stefan Monnier]

>> % emacs -Q
>> TOTORO TOTO M-b
>> C-r C-w RO
>> 
>> this fails to find "TOTORO" because we end up looking for "totoRO"
>> (without ignoring case) rather than "TOTORO".

> Sorry, I don't know how to solve this puzzle.  The value `not-yanks'
> of `search-upper-case' explicitly tells Isearch to downcase the word
> pulled from the buffer.

I know, but I think it's wrong.  I think that rather than downcase it,
it should only cause the case to stay ignored.  The behavior I'd expect
is something like:

- C-r C-w leads to "I-search: toto", which hides the uppercase nature of
  the yanked string, but doesn't actually throw it away.
- then typing "RO" leads to "I-search: TOTORO", where TOTO's uppercase
  nature is made explicit.


        Stefan