[MERGE] ``bzr check`` CLI improvements

[Ian Clatworthy]

Daniel Mark Watkins wrote:
> The attached allows the user to specify whether they want to check the
> branch, the repository or the working tree (or some combination
> thereof) at the specified location.  If nothing is specified, it checks
> everything.
> 
> It builds on my fix for bug #64783.
> 

Please update the help for the check command to explain the behaviour
when none of the (new) flags are given. Maybe add some examples as well.

My main concern with the way you've implemented this is that running

  bzr check --tree

on a repository will silently do nothing. I'd expect it to complain. I
guess I'm saying that explicitly asking for a check that can't be done
isn't the same thing UI wise as "do the best you can at the given path".
It's not something I feel strongly enough about to reject the patch
on - what's you've done is a step forward - but I'd be happier if you
came up with a solution.

Perhaps pass the things to check as a dict or set and None can mean all?

Ian C.