Performance optimization: `yield` with an implicit `block` is faster than `block.call`.
See http://youtu.be/fGFM_UrSp70?t=10m35s and the following benchmark:

```ruby
require 'benchmark/ips'

def fast
 yield
end

def slow(&block)
 block.call
end

Benchmark.ips do |x|
 x.report('fast') { fast{} }
 x.report('slow') { slow{} }
end

# => fast    154095 i/100ms
# => slow     71454 i/100ms
# =>
# => fast  7511067.8 (±5.0%) i/s -   37445085 in   4.999660s
# => slow  1227576.9 (±6.8%) i/s -    6145044 in   5.028356s
```

Add a deprecation warning for abiguous boolean values

In Rails 5.0, we'd like to change the behavior of boolean columns in
Rails to be closer to Ruby's semantics. Currently we have a small set
of values which are "truthy", and all others are "falsy". In Rails 5.0,
we will reverse this to have a small number of values which are "falsy",
and all others will become "truthy".

In the interim, all values which are ambiguous must emit a deprecation
warning.

A warning line should look like a warning section in Guides

Clarify wording in Rails HTML Sanitizer section [ci skip]

[ci skip]

Fix example code for `Rails::Generators::Testing::Behaviour` [ci skip]

`cleanup_destination_root` method is not found anywhere.
Instead, `prepare_destination` clean up distination root on setup.

Closes #17197.
Closes #17207.

`{required}` is a type modifier so it should be:

    user:references{required}:index

and not:

    user:references:index{required}

mention the :without option [ci skip]

As pointed out in the ActiveModel::Validations::HelperMethods #validates_format_of documentation.

clarify debugger platform invocation

The behavior has changed since 4.1 and non-array values are no
longer type casted to a blank array. This way the user can define
custom validations on that property.

[ci skip] add AC::InvalidCrossOriginRequest to list of rescue_responses default

/cc @sgrif

remove unneeded file from Railties.

use require_command! instead of calling its definition

In the DSL you can now do:

create_table(:foos) do |t|
  t.bigint :hi
end

Fix typo in actionpack/lib/action_dispatch/routing/mapper.rb [ci-skip]

Raise an error for has_one associations which try to go :through a polymorphic association

ActionController::InvalidCrossOriginRequest fails with 422 instead of 500

Fix how file_ and password_field_tag edit options

This commit fixes the behavior of `file_field_tag` and `password_field_tag`
when invoked with a hash of options.

These two helpers are different from all the other ones in that they modify the
options hash passed as a parameter, whereas all the other helpers duplicate it
before updating it.

The result is that *bad things* can happen if the user re-uses the same hash.
For instance, users who write the following code to display a file field
followed by a text field (both with the same class):

```rhtml
<% options = {class: 'important'} %>
<%= file_field_tag 'Upload', options %>
<%= text_field_tag 'Name', options %>
```

would instead see **two file fields!**

```html
<input class="important" id="Upload" name="Upload" type="file">
<input class="important" id="Name" name="Name" type="file" value="value">
```

This PR replaces `update` with `merge` in the code of the two helpers,
fixing the issue above.

The included test verifies the change, since it passes after this PR, but
fails before with the following error:

```
Expected: <input type="text" name="title" id="title" value="Hello!" class="important" />
Actual: <input type="password" name="title" id="title" value="Hello!" class="important" />
```

delete leftover JoinOperation struct

Remove duplicate stringify_keys in text_field_tag and number_field_tag

All the methods that invoke `text_field_tag` (such as `hidden_field_tag`)
and all the methods that invoke `number_field_tag` (that is `range_field_tag`)
do not need to call `stringify_keys` on their `options` parameter since the
`text_field_tag` method [is already doing it internally](https://github.com/claudiob/rails/blob/4159134524f4c78d008eef9d9a17f73a3172dcc8/actionview/lib/action_view/helpers/form_tag_helper.rb#L182):

```ruby
def text_field_tag(name, value = nil, options = {})
  tag :input, { "type" => "text", "name" => name, "id" => sanitize_to_id(name), "value" => value }.update(options.stringify_keys)
end
```

and `number_field_tag` is [already doing it internally](https://github.com/claudiob/rails/blob/e3207bdbba55f3806441f22b175557579bc0b051/actionview/lib/action_view/helpers/form_tag_helper.rb#L780) as well:

```ruby
def number_field_tag(name, value = nil, options = {})
  options = options.stringify_keys
  ...
end

[Note #1: My code uses `merge` to respect the existing behavior of
duplicating the `options` hash before updating its keys, see https://github.com/rails/rails/pull/17096#issuecomment-57223827]

[Note #2: My code uses symbols instead of strings (e.g.: `:hidden`) to look
forward to future version of Ruby/Raiks (GC symbols); the result of the method,
however, is the same, because the symbols are stringified inside `text_field_tag`]

[Note #3: I had previously created a similar PR #17096 but decided to
split it into multiple PRs given the feedback received in the comments]

Use `#tr` instead of `#gsub` in Journey scanner

Add ActiveJob to "Welcome to Rails" section