bug#18406: O_NOATIME patch

[Paul Eggert]

> If the patch is of interest I'm willing
> to improve it by having the feature
> present conditionally on the appearance of
>     HAVE_WORKING_O_NOATIME
> in 'config.h'.

Thanks, but there's no need for that; just have 'grep' complain if the 
option is used and O_NOATIME == 0.

I'm of two minds about this suggestion.  On the one hand we don't want 
to add an option like this to every utility that reads files. On the 
other hand grep is used soooo often that it may be justifiable.  What do 
other people think?

If we add it, it should not have a single-letter option, though, and the 
long option should be called "--atime-preserve" for compatibility with 
tar, and the patch should also use FTS_NOATIME to avoid updating atime 
on directories with grep -r, and it should be documented properly in 
grep.texi and in 'grep --help' output and in NEWS (plus maybe write a 
test case or two....).