bug#31228: Update GREP manpage

[Paul Eggert]

Ingo Schwarze wrote:

> i admit that it requires a bit of work, but it would
> give your users better manual pages

We could add it to our list of things to do. In the meantime...

> groff and mandoc output of what you committed to git are
> byte-by-byte identical except for the following one-blank difference
> (mandoc output looks minimally better than groff output at that
> point, groff prints one excess blank character because it wrongly
> detects the end of a sentence where there is none):

That's a minor formatting glitch in the grep man page. Thanks for reporting it. 
I fixed it by installing the attached patch, which fixes some similar glitches 
too. I installed a couple of other man page patches while in the neighborhood; 
you can see the current version here:

https://git.savannah.gnu.org/cgit/grep.git/plain/doc/grep.in.1

0001-doc-man-page-format-fixes.patch
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