Fix bug in LevelDB datastore's Delete() method.
Fix bug in LevelDB datastore's Delete() method.

LevelDB Delete() method will not return ErrNotFound, so check that the
key exists first by calling Has() and return ds.ErrNotFound if Has()
returns false.

License: MIT
Signed-off-by: Kevin Atkinson <13fbd79c3d390e5d6585a21e11ff5ec1970cff0c@kevina.org>

jbenet/go-datastore