[Rebuild] Extending Richard's "v0 for relations" suggestion

[Ed Loach]

> * In a merge, if tags were copied from a merged (deleted) way, it
is
> worth considering whether the tags were clean. However, the v0
> approach
> doesn't help with that.

No, but in the case that ways are merged, you will
a) have a pre-merged way which had tags
b) someone doing the merging who has either accepted or not who has
taken the decision which tags to change. 

So, if tags change as a result of a merge, you can treat it as any
other tag change on any way - base whether things are clean or not
on the accepted status of the mapper.

This logic might fall down where they just let JOSM merge everything
separated by ; but you could still argue they have decided to make
that change.

Ed