A previous patch (/r/9068/) updated Review.save to pass along all

keyword arguments, such as update_fields. However, we were still

always updating the timestamp field on the model, even if it wasn't

being saved to the database. This lead to inconsistencies between fields

on objects and fields in the database, causing a test failure. We now

only update the timestamp field specifically when we are updating all

fields or include timestamp in update_fields so that this does not

happen.

With this patch applied, all unit tests pass.