* Revert previous changes
* s3: use cursor to track tree traversal
fix https://github.com/seaweedfs/seaweedfs/issues/3166
* special cases for empty prefix and empty directory
* use constants
* address empty folder
* undo local changes
* fix IsTruncated
* adjust counting directories
* fix cases when prefix is a directory
* s3: handle directory object
works for
aws --endpoint-url http://127.0.0.1:8333/ s3api list-objects-v2 --bucket test --prefix "fakedir"