kiji-express: EXP-371. EntityId equality, hashing, and comparison needs work

issue: https://jira.kiji.org/browse/EXP-371
review: https://review.kiji.org/r/1587
commit: https://github.com/kijiproject/kiji-express/commit/f97e0b4798cd0d12a4dd8a97ac4eeb3b633b4ab1