commit: Correct case-insensitive search for non-case, non-ASCII chars. Add tests.

[Aidan Kehoe]

 Ar an t-aonú lá is triochad de mí Eanair, scríobh Michael Sperber: 

 > Let me know if you need more info---I couldn't convince gdb on my Mac OS
 > X box to produce a backtrace right away, but I'll have more time
 > tomorrow.

Ideally, I’d like the entire buffer being searched, together with the output
of M-: (current-case-table) RET, both saved using escape-quoted. I can’t
provoke an assertion failure with 

(search-forward "Patrick Mézard <pmezard at gmail.com>" nil t)

on its own, so I need more context.

-- 
¿Dónde estará ahora mi sobrino Yoghurtu Nghé, que tuvo que huir
precipitadamente de la aldea por culpa de la escasez de rinocerontes?