Cherry-pick b2db07afe441a49560ed2b330bf5f10979bf4326 from fmarczin.
Cherry-pick b2db07afe441a49560ed2b330bf5f10979bf4326 from fmarczin.

Does not import tests and keeps the _unmap_key assertion.

fmarczin/simplekv,karteek/simplekv,mbr/simplekv,mbr/simplekv,karteek/simplekv,fmarczin/simplekv