Propagate test messages through assert_routing helper, Fixes #14908

assert_routing was not raising the message passed into the assertion
violation that it raised. This change propagates messages through
the on_fail error.

This fixes this error:
https://github.com/rails/rails/issues/14908

A test case for this issue is located here.
https://github.com/estsauver/test14908

To see that test case fail in the example app, just run
ruby -Itest test/controllers/guests_controller_test.rb
reset_column_infomation shouldn't be part of the assertion.
Fix setting a polymorphic association's attributes to nil and saving, if that association had been non-nil and loaded.

This raised a nil deref, because the stale_state test returned true (the target was no longer valid) and so #find_target called #scope, which ran klass.all - which failed because #klass is now nil.

This only happened if saving the record holding this polymorphic association, as opposed to say referencing the association, because the latter is implemented by the SingularAssociation#reader method which called #reload if the target was stale.  This patch does something similar, but a bit less radical (calling reset).
recount files quantity
[ci skip ]Document transform_values && transform_values!
[ci skip] document truncate_words
code quotes for classname
[ci skip] wrap to 80 chars
[ci skip] docs asset_pipeline#CDNs
[ci skip] docs asset_pipeline CDN set up
[ci skip] docs CDN caching behavior
[ci skip] docs CDN header debugging
[ci skip] docs CDN Cache-Control behavior
[ci skip] docs can URL cache invalidation
[ci skip] fix grammar in docs
Fix typo in ActiveJob guide [ci skip]
[ci skip] use NOTE instead of Note
[ci skip] proper end to sentence
[ci skip] docs grammar
Highlight Class/Module [ci skip]