Change some guarantee_errs to guarantees.
Show result code in guarantee.
Makes deserialization assertions more informative.
Remove a guarantee that survived the purge.
Merge branch 'remove_guarantee_errs' into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next