As of https://github.com/rails/rails/commit/e781aa31fc52a7c696115302ef4d4e02bfd1533b SQLite3Column has been dropped.

[Andrey Novikov & Łukasz Sarnacki]

The fixtures are still in play, adding a new column without a default and `null: true`
is not possible. This reverts back to leaking global state, as our `schema.rb` adds
the `null: false` constraint on this field.

A future solution would be to make the `migration_test.rb` run independent of fixture tables.
This way we can simply drop the state after test execution, without worrying about side effects.

/cc @zuhao

We are planning to remove mocha from our test suite because of
performance problems. To make this possible we should stop require mocha
on ActionSupport::TestCase.

This should not affect applications since users still need to add mocha
to Gemfile and this already load mocha.

Added FIXME notes to place that still need mocha removal

Before this change, create_join_table would not remove the common prefix
in the join table name, unlike ActiveRecord::Reflections. A HABTM
between Music::Artist and Music::Record would use a table
music_artists_records, while create_join table would create
music_artists_music_records.

These tests were passing before because the precision were not using to
cast the value. Not it is being used so it would fail on sqlite3

One of the branches is using a proc to check if the value respond_to a
method so it is better to not do case comparations

Same as we did for collection, removed the `@macro` instance var
and it is now set in each association. Unfortunately it can't be
left undefined in AssociationReflection so it has to be set there.
For now I am setting it to NotImplementedError since there is no
default macro and it changes based on the reflection type.

This option is unused, left over from pre-1.0 Rails to internally distinguish the location of the foreign key.

This reverts commit babc24c1.

Conflicts:

	activerecord/test/cases/adapters/mysql/connection_test.rb
	activerecord/test/cases/adapters/mysql2/connection_test.rb

This is a follow up to f8f5cdc9

This is a follow-up to 3121412c

/cc @rafaelfranca

This will remove deprecation warnings from the PostgreSQL suite:

```
DEPRECATION WARNING: #capture(stream) is deprecated and will be removed in the next release. (called from capture at /Users/senny/Projects/rails/activesupport/lib/active_support/core_ext/kernel/reporting.rb:89)
/Users/senny/Projects/rails/activesupport/lib/active_support/core_ext/kernel/reporting.rb:89:in `capture'
  /Users/senny/Projects/rails/activerecord/test/cases/adapters/postgresql/composite_test.rb:73:in `ensure_warning_is_issued'
  /Users/senny/Projects/rails/activerecord/test/cases/adapters/postgresql/composite_test.rb:48:in `test_column'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:106:in `block (3 levels) in run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:204:in `capture_exceptions'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:103:in `block (2 levels) in run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:256:in `time_it'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:102:in `block in run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:317:in `on_signal'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:276:in `with_info_handler'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest/test.rb:101:in `run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:759:in `run_one_method'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:293:in `run_one_method'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:287:in `block (2 levels) in run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:286:in `each'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:286:in `block in run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:317:in `on_signal'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:306:in `with_info_handler'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:285:in `run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:149:in `block in __run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:149:in `map'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:149:in `__run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:126:in `run'
  /Users/senny/Projects/rails/.bundle/gems/minitest-5.3.3/lib/minitest.rb:55:in `block in autorun'
```

These methods are not random so they should not belings to SecureRandom
module.

These methods may cause confusion with the `reset_changes` that
behaves differently
of them.

Also rename undo_changes to restore_changes to match this new set of
methods.

While running the spec `ARCONN=mysql2 ruby -v -Itest
test/cases/yaml_serialization_test.rb`
the following warning shows up:
`implementing to_yaml is deprecated, please implement "encode_with"`

This method name is causing confusion with the `reset_#{attribute}`
methods. While `reset_name` set the value of the name attribute for the
previous value the `reset_changes` only discard the changes and previous
changes.

Also updated the test case to reflect that

Fixed JSON coder when loading NULL from DB

This reverts commit 6f3c64ee.

Conflicts:
	activerecord/CHANGELOG.md