previously dynamic finders only worked in combination with the actual
column name and not its alias defined with #alias_attribute

Get rid of ActiveModel::Configuration, make better use of
ActiveSupport::Concern + class_attribute, etc.

prevent users from unknowingly using bad regexps that can compromise security (http://homakov.blogspot.co.uk/2012/05/saferweb-injects-in-various-ruby.html)

* Moved the simplest case--enable/disable all on all--to the top.
* Made clear what "ORM" means to avoid having to teach people how to solve "uninitialized constant ORM"
  errors in their test reports.

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.

Passing a falsey option value for a validator currently causes that validator to
be enabled, just like "true":

    ActiveModel.validates :foo, :presence => false

This is rather counterintuitive, and makes it inconvenient to wrap `validates` in
methods which may conditionally enable different validators.

As an example, one is currently forced to write:

      def has_slug(source_field, options={:unique => true})
        slugger = Proc.new { |r| r[:slug] = self.class.sluggify(r[source_field]) if r[:slug].blank? }
        before_validation slugger
        validations = { :presence => true, :slug => true }
        if options[:unique]
          validations[:uniqueness] = true
        end
        validates :slug, validations
      end

because the following reasonable-looking alternative fails to work as expected:

      def has_slug(source_field, options={:unique => true})
        slugger = Proc.new { |r| r[:slug] = self.class.sluggify(r[source_field]) if r[:slug].blank? }
        before_validation slugger
        validates :slug, :presence => true, :slug => true, :uniqueness => options[:unique]
      end

(This commit includes a test, and all activemodel and activerecord tests pass as before.)

This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

XmlMini define the xml 'datatime', but according to
http://www.w3.org/TR/xmlschema-2/#dateTime could be better
change this to 'dateTime' with upper case letter 'T.
So 'DateTime' and 'Time' are redefined from 'datetime' to 'dateTime'

add the changing to the changelog

This reverts commit cae1ca7d, reversing
changes made to da97cf01.

These changes break the build, it needs more investigation.

For future reference, this is the regex I used: ^\s*#\s*\n(?!\s*#). Replace
with the first match, and voilà! Note that the regex matches a little bit too
much, so you probably want to `git add -i .` and go through every single diff
to check if it actually should be changed.

When a model nests another model that also nests yet another model
using accepts_nested_attributes_for method, its Errors object can
have an attribute name with "contacts.addresses.street" style.

In this case, the dots within the namespace should be substituted
with slashes so that we can provide the translation under the
"activemodel.attributes.person/contacts/addresses.street" key.

This commit is related to #3859.