In restic <0.10.0, it was possible that the blobs of a pack file were
split across multiple indexes. `MasterIndex.Rewrite` however assumed
that each an index always contains the full description of a pack file.
Therefore, further index entries for a pack were filtered out as
duplicates. Now, the code also checks the blobs contained in the index
entry while filtering out duplicates.
Michael Eischer
5b39ad861e