Similar to dangerous attribute methods, a scope name conflict is
dangerous if it conflicts with an existing class method defined within
`ActiveRecord::Base` but not its ancestors.

See also #13389.

*Godfrey Chan*, *Philippe Creux*

Before:

  >> ActiveRecord::Base.respond_to?(:find_by_something)
  NoMethodError: undefined method `abstract_class?' for Object:Class

After:

  >> ActiveRecord::Base.respond_to?(:find_by_something)
  => false

Allow session serializer key in config.session_store

MessageEncryptor has :serializer option, where any serializer object can
be passed. This commit make it possible to set this serializer from configuration
level.

There are predefined serializers (:marshal_serializer, :json_serialzier)
and custom serializer can be passed as String, Symbol (camelized and
constantized in ActionDispatch::Session namepspace) or serializer object.

Default :json_serializer was also added to generators to provide secure
defalt.

Correctly send the string given to lock! and reload(:lock) to the lock scope - fixes #13788

As per the documentation at lock!, if the :lock option is a string it should use the given SQL to generate the lock statement.

Added documentation for css_compressor in asset_pipeline.md

Log for which keys values were set to nil in deep_munge

Handle aliased attributes in AR::Relation#select, #order, etc.

With this we can write `Model#select(:aliased)`, `Model#order(:aliased)`,
`Model#reoder(aliased: :desc)`, etc.

Supplementary work to 54122067.

deep_munge solves CVE-2013-0155 security vulnerability, but its
behaviour is definately confuisng. This commit adds logging to deep_munge.
It logs keys for which values were set to nil.

Also mentions in guides were added.

Add docs about behaviour of replacing a has_one associate object.

Add docs about behaviour of replacing a has_one associate object, that the previous one is deleted even if the new one
 doesn't get persisted to database.

 Fixes #13197 . [ci skip]

Replace File.exists? with File.exist?

To quell warnings on ruby 2.1

use the new clear_validators! api everywhere to reset validators in tests

Rails config for raise on missing translations

The request attributes filtered_parameters, filtered_env and filtered_path
are memoized for performance reasons. However this can cause unusual
behavior in tests where there are multiple calls to get, post, etc.

Fixes #13803.

Ability to specify multiple contexts when defining a validation.

Add a config to setup whether raise exception for missing translation or
not.

Display value when raising due to unscope() issues

Example:

validates_presence_of :name, on: [:update, :custom_validation_context]

Ruby on Rails 4.1 Release Notes: Fix spelling [ci skip]

Hopefully make it easier to debug errors. e.g

Before:

    RuntimeError:
       unscope(where: "deleted_at") failed: unscoping String is unimplemented.

After:

    RuntimeError:
       unscope(where: "deleted_at") failed: unscoping String "'t'='t'" is unimplemented.

Both Time#xmlschema and DateTime#xmlschema can accept nil values for the
fraction_digits parameter. This commit makes this so for TimeWithZone
values as well.