This removes them from the public interface. The latter now only
provides the PackBlob interface, without being bound to the type used
internally by the pack package.
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.
Those methods now only allow modifying snapshots. Internal data types
used by the repository are now read-only. The repository-internal code
can bypass the restrictions by wrapping the repository in an
`internalRepository` type.
The restriction itself is implemented by using a new datatype
WriteableFileType in the SaveUnpacked and RemoveUnpacked methods. This
statically ensures that code cannot bypass the access restrictions.
The test changes are somewhat noisy as some of them modify repository
internals and therefore require some way to bypass the access
restrictions. This works by capturing an `internalRepository` or
`Backend` when creating the Repository using a test helper function.
Michael Eischer
Martin Smith