Add support for reverse query parameter in account listings

[tipabu]

No description provided.

[edmc-ss]

It is certainly possible to iterate a directory in either direction.
The semantics of the current "readdir" API only proceeds forward... and that is the way SMB & NFS would use it. But for other clients (e.g. pfs_middleware), would could certainly pass an option to reverse it. Note that this would flip the semantics of the equivalent of the "marker" as it currently marks the "last returned" rather than the "next to return" item index/name.