This change renames directories in preparation for the great package
rename. The repository is now in a broken state because the code
itself hasn't been updated. However this should ensure that git
correctly preserves history for each file.
In [] I made Registry a BGR in prep for each Registry being in
its own entity group. But we decided not to do that, and in []
mcilwain@ moved Registry under the cross-tld root. So there's no reason
for Registry to implement BackupGroupRoot anymore.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120402417
Also adds tests for currency consistency for other costs, and cleans
up some of the testing for negative currencies (since I was there).
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120231198