LogicalConstraint: typo in comment

Change-Id: I62345763e42832e2575f492a9678dbb0cfb65ec6
Merge "LogicalConstraint: typo in comment"
Change sorted.KeyValue.Find to take an optional end bound; add tests.

The new package sorted/kvtest provides a generic KeyValue test for all
implementations. Memory, SQLite, and kvfile now use it.

This speeds up the index slurping start-up of my personal Camlistore
server from 30 seconds (when it was doing 17,000+ queries in small
windows) to now just 5 seconds. That 5 seconds can be improved yet
further.

Change-Id: Idd55ba9ccd3ed12a26868a41db1af676aff7b67b
Merge branch 'master' of https://camlistore.googlesource.com/camlistore