bug#10118: C-w folds case too eagerly

[Juri Linkov]

>    % 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.