`mr config` has confusing behavior when used with chained mrconfig files.

For example, I have ~/.mrconfig which defines a git-annex repository.
And chains to ~/src/.mrconfig, which defines a git-annex repisoitory too.
Those are separate repositories in different locations. But, if
I run `mr config git-annex checkout`, it prints out the checkout
actions for both repositories.

Another example, my ~/.mrconfig defines a "." repository, which goes
in my $HOME. If I run `mr config . checkout`, it prints out the checkout
command for that repsitory, even when I'm in some other repository. Which
is pretty confusing behavior!

This might be especially bad when using mr config to change settings.
I have not dared to try it.

Looking at the code to `sub config`, it just iterates over each config
and if it contains a section named like the basename of the repository,
prints its config.

To fix it, it seems that it would need to pay attention to where it's
run. This would be a behavior change, and there's some chance it might
break something.
--[[Joey]]
