TypeError Regexp#match?(nil) in Ruby Head

I want to start reducing the calls to `lookup_context`.  That method
caches the lookup context in an ivar, but I would like to cache the
lookup context on the stack.  That way we aren't coupled to the behavior
of the `lookup_context` method.

This basically reverts c4d1a4ef

Don't use remove_method or remove_possible_method just before a new
definition: at best the purpose is unclear, and at worst it creates a
race condition.

Instead, prefer redefine_method when practical, and
silence_redefinition_of_method otherwise.

This reverts commit 3420a145, reversing
changes made to afb66a5a.

* Allow a default value to be declared for class_attribute

* Convert to using class_attribute default rather than explicit setter

* Removed instance_accessor option by mistake

* False is a valid default value

* Documentation

Actually, private methods cannot be called with `self.`, so it's not just redundant, it's a bad habit in Ruby

Regexp#match? should be considered to be part of the Ruby core library. We are
emulating it for < 2.4, but not having to require the extension is part of the
illusion of the emulation.

Mainly around `nil`

[ci skip]

All indentation was normalized by rubocop auto-correct at 80e66cc4.
But comments was still kept absolute position. This commit aligns
comments with method definitions for consistency.

All indentation was normalized by rubocop auto-correct at 80e66cc4.
But heredocs was still kept absolute position. This commit aligns
heredocs indentation for consistency.

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

Where appropriate, prefer the more concise Regexp#match?,
String#include?, String#start_with?, or String#end_with?

Also document return values for Proc/Symbol arguments

Before we were changing the state of the lookup_context for the duration
of the with_layout_format block, but since we already know the formats
we can just pass it explicitly.

Related with 8d7ce0f2

This reverts commit a9d58c77, reversing
changes made to 041c2c87.

Reason: The old behavior is how it was working in previous version of
Rails since 4.0.x so it is not safe to backport to a stable branch.

See https://github.com/rails/rails/issues/19626#issuecomment-89862258
and https://github.com/rails/rails/pull/15050#issuecomment-45333449

This commit fixes issue #19626
Don't need to check layout conditions if there is no condition

test for parent layout bug fix

This is an option for to HTML content with a content type of
`text/html`. This rendering option calls `ERB::Util.html_escape`
internally to escape unsafe HTML string, so you will have to mark your
string as html safe if you have any HTML tag in it.

Please see #12374 for more detail.

This is as an option to render content with a content type of
`text/plain`. This is the preferred option if you are planning to render
a plain text content.

Please see #12374 for more detail.

This is an option for sending a raw content back to browser. Note that
this rendering option will unset the default content type and does not
include "Content-Type" header back in the response.

You should only use this option if you are expecting the "Content-Type"
header to not be set. More information on "Content-Type" header can be
found on RFC 2616, section 7.2.1.

Please see #12374 for more detail.