add instance_accessor option to ActiveSupport::Configurable#config_accessor

Changes:

* Add `instance_accessor` option to opt out of the instance writer and
  instance reader methods.
* Raises a NameError if the name of the attribute is not valid.
* Update documentation and tests.
* Add CHANGELOG entry in activesupport.
bundle exec rake assets:precompile shouldn't fail quietly.

If JavaScript runtime is not installed, execjs fails with error quietly,
while tests continue to run. This should not happen since it causes tests
to fail for unknown reason (#6621).

This commit assures that if JavaScript runtime is not installed, an assertion
is raised.
Merge pull request #6638 from frodsan/config_accessor

add instance_accessor option to config_accessor
Merge pull request #6627 from Vanuan/tests_add_precompile_failure_assert

bundle exec rake assets:precompile shouldn't fail quietly.
Eliminate dependency on Rails::VERSION::STRING

To facilitate the use of ActiveSupport::Testing::Performance outside
of a Rails application conditionally check for the presence of
Rails::VERSION::STRING before including it in the environment string.
add :nodoc: to AS::NumberHelper private methods [ci skip]
Document ActiveSupport::JSON.parse_error [ci skip]
change AMS::JSON.include_root_in_json default value to false

Changes:

* Update `include_root_in_json` default value to false for default value
  to false for `ActiveModel::Serializers::JSON`.
* Remove unnecessary change to include_root_in_json option in
  wrap_parameters template.
* Update `as_json` documentation.
* Fix JSONSerialization tests.

Problem:

It's confusing that AM serializers behave differently from AR,
even when AR objects include AM serializers module.

    class User < ActiveRecord::Base; end

    class Person
      include ActiveModel::Model
      include ActiveModel::AttributeMethods
      include ActiveModel::Serializers::JSON

      attr_accessor :name, :age

      def attributes
        instance_values
      end
    end

    user.as_json
    => {"id"=>1, "name"=>"Konata Izumi", "age"=>16, "awesome"=>true}
    # root is not included

    person.as_json
    => {"person"=>{"name"=>"Francesco", "age"=>22}}
    # root is included

    ActiveRecord::Base.include_root_in_json
    => false

    Person.include_root_in_json
    => true

    # different default values for include_root_in_json

Proposal:

Change the default value of AM serializers to false, update
the misleading documentation and remove unnecessary change
to false of include_root_in_json option with AR objects.

    class User < ActiveRecord::Base; end

    class Person
      include ActiveModel::Model
      include ActiveModel::AttributeMethods
      include ActiveModel::Serializers::JSON

      attr_accessor :name, :age

      def attributes
        instance_values
      end
    end

    user.as_json
    => {"id"=>1, "name"=>"Konata Izumi", "age"=>16, "awesome"=>true}
    # root is not included

    person.as_json
    => {"name"=>"Francesco", "age"=>22}
    # root is not included

    ActiveRecord::Base.include_root_in_json
    => false

    Person.include_root_in_json
    => false

    # same behaviour, more consistent

Fixes #6578.
Fixed the application_controller require_dependency path generated by the app generator
Merge pull request #6643 from fredwu/fix_require_dependency

Fixed the application_controller require_dependency path generated by the app generator
Make method name consistent with existing methods
fix meaningless test case

Module#instance_methods returns an Array of Symbols in Ruby >= 1.9
So this was not actually testing anything
Merge pull request #6644 from amatsuda/fix_meaningless_test_case

fix meaningless test case
stop `to_s`ing method names

Module#methods are Symbols in Ruby >= 1.9
Symbol responds_to :upcase & :downcase in Ruby >= 1.9
no need to to_s here. Both String and Symbol can be interpolated into String
MiniTest::Spec shipped with Ruby >= 1.9.3 always responds_to __name__
Merge pull request #6647 from amatsuda/192_minitest_method_name

MiniTest::Spec shipped with Ruby >= 1.9.3 always responds_to __name__
reduce number of Strings
Merge pull request #6645 from amatsuda/reduce_string_instance

Reduce number of String instance