Unhelpful changes_display_dict output for m2m changes #800
Description
For changes to many-to-many fields, the changes_display_dict method always returns ['type', 'objects', 'operation'] rather than telling you what the actual changes are.
This is because the changes_dict entry contains something like {'type': 'm2m', 'objects': ['FOO'], 'operation': 'add'}, and the changes_display_dict method tries to turn that into something "human readable" just by iterating over it... iterating a dict just gives you the keys.
Related to #585.
I'm not sure what the answer is though, because it isn't obvious how you'd return m2m changes as a tuple, and returning some other type would be a breaking change.
Is this something that other people already have workarounds for (other than just implementing your own version of changes_display_dict)?