Tagging 5.1.6

Backport #4350 to 5.1.0-stable

When I call `#reload` on a document, I expect the data to be reloaded
from the server, even if query caching is enabled.

Backport #4295 to 5.1.0-stable

Fix : map_reduce read mode is forced to "primary"

MONGOID-4365 Only load the docs necessary for the Enumerable method called

MONGOID-3490 Handle localized boolean fields correctly in 5.1.0-stable

MONGOID-4360 Only include the match on a field once in aggregation pipeline

MONGOID-3407 Fix setting a hash field with atomic operator

Refactor inclusions

MONGOID-4315 Eager load objects when criteria docs are enumerated multiple times

MONGOID-4315 There is no reason to not eager load relations when different methods triggering queries are called on Criteria