bug#38044: 27.0.50; There should be an easier way to look at a specific vc commit

[Juri Linkov]

> The approach LGTM. I'd have used "describe" or "show", but it's not
> important.

The name vc-print-revision was modeled after vc-print-log,
vc-print-root-log, vc-print-branch-log that are not the best names
but at least consistent for their prefix.

>>      (setq default-directory rootdir)
>
> This probably needs a saving (let ((default-directory default-directory))
> ...) above it.

This is intentional because on testing I discovered that RET
on the diff part of the buffer can't visit source files
when default-directory is not root.

>> +                   (read-shell-command
>> +                        "Show revision with command: "
>> +                        (format "%s %s" vc-git-program
>> +                                (mapconcat 'identity args " "))
>> +                        'vc-git-history)
>> +                   " " t))))
>
> If wonder if some user someday is going to try and input there something
> that doesn't start with 'git '.

Someone might want to use a wrapper script.