ndb: only validate signature if don't have the note already (William Casarin)

ndb: actually write notes to DB (William Casarin)

ndb: close db after threads (William Casarin)

ndb: add ndb_lmdb struct (William Casarin)

ndb: define dbi's (William Casarin)

pushed to nostrdb:refs/heads/master

http://git.jb55.com/nostrdb/commit/181d8d5a9b352a1f88a0cffdf7652c9a4b386e89.html