bug#31228: Update GREP manpage

[Paul Eggert]

On 04/20/2018 09:03 AM, Laura Morales quoted Ingo Schwarze as writing:
> 1. BEST: Switch to the better mdoc(7) language which does provide
> such markup.

This does not work with Solaris nroff and troff, which we'd still like 
to port to, as Solaris is still a live platform.

> 2. If they insist on using the obselete man(7) language and
> want to remain portable, use standard macros like .I and
> .B and accept that no hyperlinks will appear. It is
> a limitation of the chosen language. You can't have the
> cake and eat it, too.

Although this would port, it would be less readable on newer systems. 
For example, the HTML man page wouldn't contain links to the grep 
manual. We can do better.

> 3. If they don't care about portability and live in a GNU-only
> world, use the -man-ext macros .MT and .UR, documented in
> groff_man(7). mandoc(1) implements these for GNU compatibility,
> but other formatters may not.

(3) is not as unportable as Ingo suggested, since the MT and UR macros 
can work outside the GNU environment when included in the man page. 
Please try the attached patch, which I've installed into the grep 
master. If it runs afoul of the troff subset that Ingo is using, please 
let us know and (ideally) suggest a fix.

> using \(.g to test for availability of features is
> utterly stupid. *ANY* formatter that wants to stand a chance to
> format anything properly positively *must* define it, no matter
> whether it is groff or not.

No, Solaris nroff can format the grep man page properly and it does not 
define \n(.g.

0001-doc-port-better-to-mandoc.patch
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