Skip fetching merged items without changes from TFS
`FindCommitByChangesetId` cache added
Merge pull request #569 from KindDragon/changeset_id_cache

`FindCommitByChangesetId` cache added
Test crash fixed
Merge pull request #583 from KindDragon/changeset_id_cache

Test crash fixed
Merge pull request #568 from KindDragon/improve_fetching_merge_changeset

Skip fetching merged items without changes from TFS