Conflicts:
	activerecord/lib/active_record/core.rb

This reverts commit 8d7c38b8.

Reason: Lot of the additions aren't adding value.

[ci skip]

exercise, fix typos

[getting started] dialog box is not automatic, is provided through jquery_ujs, which is necessary to have in application layout

AS::Callbacks: simplify logical statement

Remove special cases for duplicable? on Class and Module

Fix an issue with inflection

[ci skip]

<plus> is nonstandard Textile; RailsGuides::TextileExtensions::plusplus
is the method that causes multiple code-formatted `+` symbols to
generate crap like

    <code>1 <notextile><tt>+</tt></notextile> 2 ...</code>

instead of the expected output:

    <code>1 + 2 ...</code>

Fixed logger bug introduced by #2237

When Active Record has already loaded a unique association `.size` returns the wrong number.

Improve logging of ActiveModel::MassAssignmentSecurity::Sanitizer

Call methods on the correct instance in AR::Schema.define