bug#37907: --no-ignore-case option

[Karl Berry]

I suggest adding --no-ignore-case to clear the case-insensitivity -i
search. I, and surely many others, have an alias or script that runs
grep with -i by default, along with other options (since GREP_OPTIONS
was killed). It would be highly convenient to be able to add
--no-ignore-case on the fly to the rare-in-my-experience invocations
where case sensitivity is desired.

(Also, just in principle, it seems like any boolean option should be
switchable by successive options. But I won't go that far.)

Besides, since I'm not sending a patch (sorry), my expectation is that
there will never be enough time to implement random minor suggestions
like this, so it doesn't matter :).

Thanks,
Karl