Deprecate `scope_chain`

`PolymorphicReflection` needs to be custom for handling scope lambdas

Each reflection should be responsible for returning the scopes needed to
query against the db.

Update Unicode Version to 9.0.0

Also change the class_methods to ClassMethods since the former document
the method as an instance method of Parameterized not as a class method.

We own the class so we can override the initialize.

add warnings option to test runner

show correct class name in migration inherited directly error

Docs: Specify return value of `save!`

Simplify query in column_definitions() for Postgres

I can never remember if it returns `self` or `true` (seems to be `true`)

[ci skip]

Report the attribute on ActiveRecord::SerializationTypeMismatch

column_definitions() needs to fetch the collation for every column, if
present. Previously, it did so using a correlated subquery - a subquery
that references results from the outer scope.

This patch updates the query to remove the subquery in favor of a
simpler and more efficient JOIN clause.

Running the two queries through EXPLAIN against Postgres additionally
shows that the original form with a correlated subquery requires a
Nested Loop Left Join, while the new form with a simple JOIN can use a
more efficient Merge Left Join.

Improve insufficient test for `safe_join`

Needed for testing of parameterized mailers

This behavior used to warn until 2.4, and raises since 2.5.
The test here was intentinally named not to start with "test_" and so it used not to be executed because this never passes,
but now is should pass in trunk.

https://bugs.ruby-lang.org/issues/11547
https://github.com/ruby/ruby/commit/44a2576f798b07139adde2d279e48fdbe71a0148

closes #19897

Without this, the test causes a "method redefined" warning because
* first it loads I18n and defines Hash#deep_symbolize_keys inside I18n's lib/i18n/core_ext/hash.rb
* then it loads AS/core_ext/hash/keys.rb afterwards

* puma 3.7.0: to let kill("TERM") properly terminate the process in railties test (3.6.2 doesnot on my machine)
* amq-protocol 2.1.0: to reduce warnings in AJ tests
* rails-html-sanitizer: missing change in a previous commit that updated Gemfile

restore `delivery_method` after test

Currently use two variables to restore `delivery_method`, but the order
of restoring the values is incorrect and does not restore is correctly.

Fix judgment spelling [ci skip]

`judgment` is the preferred form as Rails usually follows en-us spelling
not en-gb.

make backburner integration test to work

Offer the option to use parameterization for shared processing of headers and ivars

9.0.0 was released on June 21, 2016

http://blog.unicode.org/2016/06/announcing-unicode-standard-version-90.html

http://www.unicode.org/versions/Unicode9.0.0/

There are some changes about grapheme cluster in Unicode 9.0.0:

http://unicode.org/reports/tr29/#Grapheme_Cluster_Boundary_Rules

------------

I noticed that `unpack_graphemes` returns [Other] when the argument is Other ÷ Prepend
(it must be [Other, Prepend]).
But in [Unicode 8.0.0's Prepend has no characters](http://www.unicode.org/reports/tr29/tr29-27.html#Prepend)
so we don't have to backport following patch:

```diff
should_break =
+ if pos == eoc
+   true
```

Currently, backburner integration test is not running on CI.
https://travis-ci.org/rails/rails/jobs/196005322#L610

Using `Backburner::Worker.connection` to check whether beanstalkd is
running. But `Backburner::Worker.connection` was removed in backburner
1.2.0.
https://github.com/nesquena/backburner/commit/81fde499c2263abe8dedee59a3d0e03e92d72627

Therefore, this check process always becomes false, so the test is no
longer done. I fixed it so that check processing is done correctly.