[Glass] case insensitive search broken for Unicode7

[Pieter Nagel]

Please note that Unicode16 and Unicode32 have the same problem as well.

I can confirm that the patch that Mariano Martinez Peck posted [*] works
for all three classes, at least in the sense that none of our unit tests
catch any error, and it fixes the insensitve sorting issue (for those who
don't care about using an ICU collator).

US-centric system *might* get away with patching Unicode7 alone, but then
you'd have to be pretty sure that you never deal characters beyond strict
ASCII, i.e. surnames with accented characters.

So I suggest people who need to patch Unicode7 do it to Unicode16 and
Unicode32 too.

[*] Unicode7 >> _findString: subString startingAt: startIndex ignoreCase:
aBoolean

  ^ super _findString: subString startingAt: startIndex ignoreCase: aBoolean