bug#23665: spaces in keys: doc, --debug in LC_ALL=C

[Paul Eggert]

Assaf Gordon wrote:
> 1. rephrase "key" with "sort key". Perhaps this is superfluous - thoughts ?

I would leave it alone. This is the 'sort' program, after all, so it's hard to 
misinterpret "key". Plus, "obsolescent sort key" might be misinterpreted as 
meaning a key for an obsolescent sort, not a sort key that is obsolescent.