[bug#66148] Fix Guix version number in pulled (=most) manuals

[Ludovic Courtès]

Hi!

Tobias Geerinckx-Rice <me@tobias.gr> skribis:

> Now that we use the latest release VERSION even for pulled Guixes,
> make it abundantly clear that this is a later build.
>
> * guix/self.scm (info-manual): @set the PULLED flag in version.texi.
> * doc/guix.texi (Top): Honour it.

Yeah, great initiative!

I wonder if we could avoid adding code to (guix self).  For instance,
we could have (guix self) leave ‘VERSION’ undefined and in the manual
we’d have those @inlineifset{VERSION, version @value{VERSION}, revision
from @command{guix pull}}.

How does that sound?

Ludo’.