Rather than just raising a NoMethodError when copying the config, this
commit adds a warning message until either the rails-observers gem is
installed or the relevant config options are removed.

They was extracted from a plugin.

See https://github.com/rails/rails-observers

[Rafael Mendonça França + Steve Klabnik]

Simplify String#mb_chars and fix documentation.

This behavior mattered under Ruby 1.8, but that doesn't matter now
that we don't support it.

In addition, we don't want to proxy the #class method. A test was added
to prevent against regressions.

This documentation has been out of date.

Ensure that associations have a symbol argument.

Fixes #7418.

Specify type of singular assication during serialization

When serialising a class, specify the type of any singular associations, if
necessary. Rails already correctly specifies the :type of any enumerable
association (e.g. a has_many association), but made no attempt to do so for
non-enumerables (e.g. a has_one association).
We must specify the :type of any STI association. A has_one
association to a class which uses single-table inheritance is an example of
this type of association.

Fixes #7471

Revert "rails gem has no lib directory to require"

This reverts commit 6bcbd604.

The default value for require_paths is ['lib'], and Rails does not
need to include any lib/ file to build the gem, so the previous
commit 'makes sense'. However, gems will not be built at all if
require_paths is empty (see https://gist.github.com/1065473), so
it's better to stick with the default, which does not have any
side-effects

This table is being used to verify if the :limit options is being
ignored for text and binary columns

Remove FIXME tag from abstract adapter test.

Use File.join to better integrate fixture_path in fixture_file_upload.

Cache digest opt out cleanup

Instead of deleting the skip_digest option flag, this changes the method to merely check the
key. This change is because of a discussion in this thread:

https://github.com/rails/rails/pull/8317

This commit also makes #fragment_name_with_digest private due to its
functionality being subsumed by #cache_fragment_name.

This reverts commit 33b29e01, reversing
changes made to ac8c7293.

Reason:

https://github.com/rails/rails/pull/4684#commitcomment-920313

default source in Gemfiles to :rubygems rather than hardcoding the URL

No sort Hash options in #grouped_options_for_select

* I guess this would be the preferrable default for Bundler
* current version of Bundler converts :rubygems into 'http://rubygems.org', not https://,
  and that will help those who are working on a very poor network environment that doesn't allow SSL

Fix Strong Parameters docs [ci skip]

It's only possible to inherit from ActiveRecord::Base and not include
it.

unshift html-scanner into $LOAD_PATH rather than append

Unused variable warning removed

empty rails gem's require_paths

This file was using mime_types before load the Mime::Type class.
When trying to register first Mime::Type it load mime_type that loads
mime_types in the end.

Requiring mime_type ensure that we have the class definition and the
mime types

We are already in the AR namespace, there's no way for it to be
undefined. See the cousin commit 13e72db7

Refactor a bit teardown fixtures to avoid two conditionals.

Accept symbols as #send_data :disposition value

Length validation handles correctly nil. Fix #7180

Conflicts:
	activemodel/CHANGELOG.md