Improve the docstring of case-fold-search

[Bastien]

I suggest to complete the docstring of `case-fold-search' like the
attached patch does.

In the current docstring, the expression "ignore case" is not really
appropriate because the search will not ignore uppercase characters in
the search string.  A very short way to tell this would be "*Non-nil if
searches and matches should ignore lowercase."  But while accurate, this
is confusing IMO.  Hence the long sentence in this patch, inspired by
the "Search case" section of Emacs manual.

Should I apply it?

buffer.c.patch
Description: Text Data

-- 
 Bastien