rails/rails — pull request #17139 by mfazekas (2014-10-02 08:26:52+00:00)
Title: Always reset changed attributes in becomes

When ```becomes``` changes @attributes it should also change
@changed_attributes. Otherwise we'll experience a kind of split head situation
where attributes are coming from ```self```, but changed_attributes is coming
from ```klass.new```. This affects the inheritance_colmn as it's changed by new
for example.

Fixes #16881