Consistent snapshot feature is not completely implemented

[erickt]

I noticed that inside Client::_fetch_target during the section we're updating the metadata, we're using MetadataVersion::None when getting the local target metadata, but using MetadataVersion::Hash(...) when getting the remote target metadata. Is this on purpose? If so, can you add a note to make it clear we're being inconsistent?

[heartsucker]

This is a partial bug in that the consistent_snapshot feature is not totally correct. I think this was left over because of #146. #96 was the original ticket, but it seems I missed some things.