bug#50344: C-x v keybinding for vc-print-branch-log

[Juri Linkov]

> So far we only have one tag command, and it doubles for branches with
> 'C-u'. The other tag-related command doesn't differentiate between branches
> and tags.
>
> Would having essentially two copies of these, but with different names, be
> a good idea?

It makes sense to create a copy where the meaning of its arg
is reversed, so by default it will operate on branches,
and only with C-u on tags.

> Are there some VCS which would benefit from a more stricter differentiation
> between the two? Hg, perhaps? I don't know how branches work there.

So the question is what backends already use the arg 'branchp'?
The search shows that vc-cvs-create-tag, vc-git-create-tag,
vc-hg-create-tag all use this arg.