Added ActiveRecord::Relation#none! method

Unbreak update_column/update_columns for the primary key attribute.

Didn't work before because it updated the model-in-memory first, so the DB query couldn't find the record.

Replace flow-control exception with explicit test.

Do not render views when mail() isn't called. (NullMail refactoring)

Removing JSON for other ruby

create_table raises an ArgumentError when the primary key is redefined.

AR::AttributeMethods#[] raises AM::AttributeMissingError for missing attributes

This fixes the following behaviour:

    class Person < ActiveRecord::Base
      belongs_to :company
    end

    # Before:
    person = Person.select('id').first
    person[:name]       # => nil
    person.name         # => ActiveModel::MissingAttributeError: missing_attribute: name
    person[:company_id] # => nil
    person.company      # => nil

    # After:
    person = Person.select('id').first
    person[:name]       # => ActiveModel::MissingAttributeError: missing_attribute: name
    person.name         # => ActiveModel::MissingAttributeError: missing_attribute: name
    person[:company_id] # => ActiveModel::MissingAttributeError: missing_attribute: company_id
    person.company      # => ActiveModel::MissingAttributeError: missing_attribute: company_id

Fixes #5433.

Don't log on pending migration check 

Conversation from: #6665 cc/ @rafaelfranca

fix typo in button_to helper example [ci skip]

It was noticed while profiling 'assets:precompile' in JRuby that
exception creation was consuming a large portion of time, and
some of that was due to File.atomic_write.

Testing first with File.exists? eliminates the need for an exception
which should be a perfomrance improvement on both JRuby and MRI.
In this case, the stat() isn't even extra overhead, since it is always
called.

Use the MySQL varbinary type when appropriate in migrations

button_to_function

Point the the Unobtrusive JavaScript secion in the JavaScript guide

Organize README

remove trailing whitespace within actionpack [ci skip]

fix failing isolated tests in activemodel

Fix AM::Serializers::Xml dependency