we don't handle char-downcase or char-upcase for unicode chars correctly

[kpoeck]

as Bike notes in #164

(char-downcase #\CYRILLIC_CAPITAL_LETTER_IE_WITH_GRAVE)
-> #\CYRILLIC_CAPITAL_LETTER_IE_WITH_GRAVE

[kpoeck]

In https://en.cppreference.com/w/cpp/locale/tolower and https://en.cppreference.com/w/cpp/locale/toupper are examples that should work.

This works in Xcode, so lets try this for clasp

[kpoeck]

seems to work fine:

COMMON-LISP-USER> (char-downcase #\CYRILLIC_CAPITAL_LETTER_IE_WITH_GRAVE)
#\CYRILLIC_SMALL_LETTER_IE_WITH_GRAVE
COMMON-LISP-USER> (char-upcase #\CYRILLIC_SMALL_LETTER_IE_WITH_GRAVE)
#\CYRILLIC_CAPITAL_LETTER_IE_WITH_GRAVE

[kpoeck]

Works now fine with pr #1121 merged