Fix non-intuitive repository behavior

- The SaveBlob method now checks for duplicates.
- Moves handling of pending blobs to MasterIndex.
  -> also cleans up pending index entries when they are saved in the index
  -> when using SaveBlob no need to care about index any longer
- Always check for full index and save it when storing packs.
  -> removes the need of an index uploader
  -> also removes the verbose "uploaded intermediate index" messages
- The Flush method now also saves the index
- Fix race condition when checking and saving full/non-finalized indexes

internal/repository/repack.go

@@ -84,7 +84,8 @@ func Repack(ctx context.Context, repo restic.Repository, packs restic.IDSet, kee
 					h, tempfile.Name(), id)
 			}
 
-			_, err = repo.SaveBlob(ctx, entry.Type, plaintext, entry.ID)
+			// We do want to save already saved blobs!
+			_, _, err = repo.SaveBlob(ctx, entry.Type, plaintext, entry.ID, true)
 			if err != nil {
 				return nil, err
 			}