[MERGE] Handle empty list like non-empty list in iter_changes, revert

[James Westby]

> +    * WorkingTree.revert() now accepts None to revert all files.  The use of
> +      [] to revert all files is deprecated.  (Aaron Bentley)
> +

It seems like this should go in the API BREAKS section of NEWS.

Thanks,

James

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  James Westby   --    GPG Key ID: B577FE13    --     http://jameswestby.net/
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