This fixes the restore issues as all sources will now appear as if they were originally part of the source file system.
The backend implementation has now been simplified so the backends only return names of entries with no path information. Most backends already do this, but the S3 backends did not, so this was fixed as well.
This also clears up the interfaces, so the backend does not know about the `ISourceProviderEntry`. All mapping is done by the `BackendSourceProvider`, making it simpler to support other backends as sources.
This was causing a strange issue when testing the situation where write
privileges were removed from the local destination directory. Instead
of catching the AccessViolationException and returning the expected exit
code of 100, the process would exit with Aborted (core dumped).
This concerns #4533.
Kenneth Skovhede