fuse: handle duplicate timestamps for snapshots
fuse: handle duplicate timestamps for snapshots

This closes #606, which fails because several snapshots are created with
exactly the same timestamp, and the code checks that for each snapshot
there is a dir in the fuse mount. This fails for colliding timestamps,
so we now add a suffix "-1", "-2" etc for each duplicate timestamp.

ar-jan/restic,jayme-github/restic,kurin/restic,ar-jan/restic,arithmetric/restic,ckemper67/restic,fawick/restic,middelink/restic,restic/restic,byo/restic,kurin/restic,jayme-github/restic,stuertz/restic,fawick/restic,byo/restic,restic/restic,stuertz/restic,middelink/restic