Created a method to automatically find inverse associations and cache
the results. Added tests to check to make sure that inverse associations are
automatically found when has_many, has_one, or belongs_to associations
are defined.
Merge pull request #9522 from wangjohn/automatic_search_for_association_inverses

Finding inverse associations automatically
Fix Typo existant -> existent [ci skip]
Merge pull request #10511 from prathamesh-sonpatki/existent

Fix Typo existant -> existent [ci skip]