The rails/rails gemnasium page (https://gemnasium.com/rails/rails) is not helping much.
It lists 0 dependencies so there is not much to track. Also our gems mostly depend
on other gems we control. There is not much point in monitoring them.

The batch was introduced with #3909.

As discussed in #13940 this can be removed
We can document this somewhere else in testing guides.

Fixed typos

Fixed typos in column_definition_test.rb.

This behavior was introduced since Rails 3.1 (207f266c)
but the docs were still out of date.

[ci skip]

[ci skip] Add missing 'task' to note on Running Migrations

Make sure transaction state resets after commit

add missing sharp [ci skip]

Closes #9131.

destruction errors out on HABTM w/out primary key

The documentation of `#to_key` (http://api.rubyonrails.org/classes/ActiveModel/Conversion.html#method-i-to_key)
states that it returns `nil` if there are no key attributes. `to_param` needs
to be aware of that fact and return `nil` as well.

Previously it raised the following exception:

```
  1) Error:
ConversionTest#test_to_param_returns_nil_if_to_key_is_nil:
NoMethodError: undefined method `join' for nil:NilClass
    /Users/senny/Projects/rails/activemodel/lib/active_model/conversion.rb:65:in `to_param'
    /Users/senny/Projects/rails/activemodel/test/cases/conversion_test.rb:34:in `block in <class:ConversionTest>'
```

Missing closing parenthesis. [ci skip]

[fixes #12566]

be more specific about csrf token and ajax - not whitelisted outside of jquery-rails [ci skip]

This is a follow up to #13926.

/cc @fxn

Resolve the following error when running `bundle exec rake guides:generate:html`:

```
/Users/senny/.rbenv/versions/2.0.0-p353/bin/ruby rails_guides.rb
Generating 2_2_release_notes.md as 2_2_release_notes.html
/Users/senny/Projects/rails/guides/rails_guides/helpers.rb:17:in `documents_by_section': uninitialized constant RailsGuides::Helpers::YAML (ActionView::Template::Error)
	from /Users/senny/Projects/rails/guides/rails_guides/helpers.rb:32:in `docs_for_menu'
	from /Users/senny/Projects/rails/guides/source/layout.html.erb:56:in `block in ___sers_senny__rojects_rails_guides_source_layout_html_erb___3094858039481335962_70118647133480'
	from /Users/senny/Projects/rails/guides/source/layout.html.erb:54:in `each'
	from /Users/senny/Projects/rails/guides/source/layout.html.erb:54:in `___sers_senny__rojects_rails_guides_source_layout_html_erb___3094858039481335962_70118647133480'
	from /Users/senny/Projects/rails/actionview/lib/action_view/template.rb:143:in `block in render'
	from /Users/senny/Projects/rails/activesupport/lib/active_support/notifications.rb:161:in `instrument'
	from /Users/senny/Projects/rails/actionview/lib/action_view/template.rb:337:in `instrument'
	from /Users/senny/Projects/rails/actionview/lib/action_view/template.rb:141:in `render'
	from /Users/senny/Projects/rails/actionview/lib/action_view/renderer/template_renderer.rb:61:in `render_with_layout'
	from /Users/senny/Projects/rails/actionview/lib/action_view/renderer/template_renderer.rb:47:in `render_template'
	from /Users/senny/Projects/rails/actionview/lib/action_view/renderer/template_renderer.rb:17:in `render'
	from /Users/senny/Projects/rails/actionview/lib/action_view/renderer/renderer.rb:42:in `render_template'
	from /Users/senny/Projects/rails/actionview/lib/action_view/renderer/renderer.rb:23:in `render'
	from /Users/senny/Projects/rails/actionview/lib/action_view/helpers/rendering_helper.rb:24:in `render'
	from /Users/senny/Projects/rails/guides/rails_guides/markdown.rb:160:in `render_page'
	from /Users/senny/Projects/rails/guides/rails_guides/markdown.rb:25:in `render'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:205:in `block in generate_guide'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:195:in `open'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:195:in `generate_guide'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:144:in `block in generate_guides'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:142:in `each'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:142:in `generate_guides'
	from /Users/senny/Projects/rails/guides/rails_guides/generator.rb:97:in `generate'
	from rails_guides.rb:63:in `<main>'
rake aborted!
Command failed with status (1): [/Users/senny/.rbenv/versions/2.0.0-p353/bi...]
/Users/senny/Projects/rails/guides/Rakefile:11:in `block (3 levels) in <top (required)>'
Tasks: TOP => guides:generate:html
(See full trace by running task with --trace)
```

Fixed minor typo [ci skip]

Fixes the camelCase variable name in the docs [ci skip]

Adding a documentation example and a test to button_to with path

I did not see in the docs that `button_to` supports not only URLs but paths as well. I documented this functionality with a unit tests and added an example to the docs as well.

Deprecate custom BigDecimal serialization

Conflicts:
	activesupport/CHANGELOG.md