rails/rails — pull request #12413 by arthurnn (2013-09-30 21:26:17+00:00)
Title: Inverse of on build

### Problem
When building a new relations(any type of relation) we need to setup the inverse_of association.
See https://github.com/rails/rails/issues/10371

### Solution
Call `.set_inverse_instance` on the association parent. Also remove `set_inverse_instance` from `add_to_target` on collection, as we build it before, and we dont need that extra call.

review @rafaelfranca @robin850