no-duplicate-dollar-variables: allow dup vars in unrelated scopes

[srawlins]

Fixes #277

[srawlins]

This seems to be inefficient - I think this serializes the entire subtree below [parent]. I'm not sure what to use as unique keys to traverse down the scopes though. the non-leaf nodes are all Containers I think? I couldn't find a good common way to uniquify them...

[kristerkari]

Thanks! This seems like a good fix to the rule.

[kristerkari]

There could be one additional test to check that we get a warning for .d {}, but not for the other variables:

      .a {
        $ab: 1;
      }
      .b {
        $ab: 2;
      }
      .c {
        $ab: 3;
        .d {
          $ab: 4;
        }
      }

The README of the rule should also be updated to mention that the rule considers scopes, and give an example of the scopes.

[srawlins]

Done. Additional test and README text.

[kristerkari]

Great, thanks! Going to do a new release with the currently approved PRs.