Fix – sorted limited offset mount queries

[michaelavila]

Based on: #123
Supersedes: #121

Use NaiveLimit and NaiveOffset to add limit/offset features to queries on mount.

[michaelavila]

I'm working on more tests now.

[Stebalien]

(sorry for leaving you with the annoying part)

[Stebalien]

Honestly, we could probably switch to the naive filter as well. I'm not sure why I did it this way (well, it'll be slightly faster but not by much).

[eingenito]

@Stebalien Actually we're finding that we might have to use the NaiveFilter implementation because if the underlying datastores support filter they're going to be filtering only on the subkey (if they filter on key) meaning they'll exclude their mount prefix. So we probably have to treat filters in the same way we do offsets by stashing them and then removing them from the Query that is passed to each datastore, and then applying them at then end when the keys are full keys. So we're going to do as you suggest here and use NaiveFilter. It reads a little clearer too.

[michaelavila]

There's a commit that fixes filtering by using NaiveFilter: 5b4de5b

[Stebalien]

Ah, good catch. We definitely need to remove the filters from the query we're forwarding. Actually, we should probably just create a new query.

[Stebalien]

LGTM!