bug#34949: 27.0.50; Docstring of `vc-deduce-fileset' incomplete

[Drew Adams]

> > To avoid other possible future problems, please consider
> > putting all such vc-dired commands on a VC-marking prefix
> > key, such as `* v'.
> 
> `* v' is not mnemonic for marking.  The character `*'
> has such mnemonic because `*' *is* a marking char.

Yes, `*' has that meaning.  So `* v' can have the meaning
of marking VC stuff.

See "all", above.  `* v' as a _prefix_ key, for marking
stuff in VC-dired.  And this is an example - marking
unregistered stuff (presumably).

> > E.g., use `* v u' for `vc-dir-mark-unregistered'.  `* v'
> > is currently undefined for Dired, and that way Dired
> > sacrifices only `* v', for possible Dired marking commands.