We've had a few reports of users who had problems publishing reviews or

replies, and it seems like the cause is duplicate entries being returned

by our accessible object queries used by the batch endpoint. We'd then

do a length comparison to make sure that the length of the fetched

result was the same as the length of the requested set of objects to

publish, and fail with a very unhelpful message. This is most easily

triggered by having multiple invite-only review groups assigned to a

review request.
This change fixes the problem by using Django's in_bulk() method to

aggregate the results by PK. This handles deduplication without having

to add DISTINCT to the query, which can cause performance problems in

big databases on MySQL.
A new unit test has been added which failed with the reported error

before the change, and passes after.

Manually tested on both SQLite and MySQL. Saw that it failed before

  the change and succeeded afterward.
Ran unit tests.