Implement an ETS-basd couch_lru
Use a monotonicaly incrementing counter instead of `erlang:now()`. We don't
technically need to time-based functionality and just want to know relative
insertion order.
Instead of gb_tree, use an ordered_set ETS. This keep items sorted by their
update order, with most recent ones at the bottom.
An set ETS replaces the dictionary which maintains a mapping from database
names to their entry in updates table.
Interface is the same as the old couch_lru, so it is a direct swap in.
Thanks to Eric Avdey for intial version of test module.
COUCHDB-3326
2 files changed
