Sometimes s3 listobjects for a directory includes an entry for that
directory. The restic s3 backend doesn't expect that and returns
an error.
Symptom is:
ReadDir: invalid key name restic/key/, removing prefix
restic/key/ yielded empty string
I'm not sure when s3 does that; I'm unable to reproduce it myself.
But in any case, it seems correct to ignore that when it happens.
Fixes#1068
Backup was choosing a parent snapshot that had the same tags, which
makes backup unnecessarily slow when there are newer snapshots with
different tags.
There's no reason parent has to have the same tags.
This change makes backup choose the newest snapshot instead.
Felix Lee