Merge pull request #13867 from mauricio/bug-13861

Fixing issue with activerecord serialization not being able to dump a record after loading it from YAML - fixes #13861
Aesthetic
Merge pull request #13879 from schneems/schneems/more-explicit-database-config-error

Enhance errors while retrieving database config
Implement a simple stub feature to use in the Time travel helpers
Alias the original method first to avoid warnings
Use instance method instead of before hook
Change the class and method visibility
Store the singleton_class in a local variable
Use each_value
Merge pull request #13883 from rafaelfranca/rm-time-travel

Alternative implementation to make time travel not dependent on mocha
find_in_batches should not mutate its argument
Modify the session serializer implementation

Rename allowed options to :marshal and :json, for custom serializers
only allow the use of custom classes.
Merge pull request #13888 from rails/session-serializer

Modify the session serializer implementation
docs, `references` is only used with `includes`. Closes #13727.

There is no gain in `referencing` tables that are not used for preloading.
Furthermore it will break if polymorphic associations are invloved. This
is because `references_eager_loaded_tables?` uses all `reference_values`
to decide wether to `eager_load` or `preload`.
tidy CHANGELOGs [ci skip]
Merge pull request #13878 from marcandre/leave_my_options_alone

find_in_batches should not mutate its argument
Add `travel_back` to remove stubs from `travel` and `travel_to`
Remove automatic removal of Date/Time stubs after each test case

This behavior is only work out-of-box with minitest and also add a
downside to run after each test case, even if we don't used the travel
or travel_to methods
Improve documentation [ci skip]
Merge pull request #13884 from rafaelfranca/rm-travel-back

Add `travel_back` to remove stubs from `travel` and `travel_to` and remove auto-rollback after each test case