Teach VariableProvider to expose OriginalRelease
Introduce RepositoryFixtureBase
Introduce CommitCountingRepoFixture
Turn MetaDataByCommitFixture into an acceptance test
Kill some warnings
Merge pull request #162 from Particular/ntk/migrate_MetaDataFixture

Migrate MetaDataByCommitFixture fixture and various fixes
Fine tune topological sorting

 - Use Time sorting to disambiguate ordering of parents of a merge
   commit
 - Pass to the query filter the commit boundary