Remove extra case.
Add error message for including nokogiri in Gemfile for rake doc:guides [ci skip]

- When `rake doc:guides` is run from applications, it complains for
  presence of redcarpet if it not present in Gemfile
- Similarly it should complain about nokogiri
Adds Akshay Surve to Rails Guides credits list

I had written the original guide for "A Guide to Testing Rails
Applications". The current documents maintains the same structure and
examples I had drafted albeit with some minor changes to keep up with
newer version of Rails.

Older version which had credits included:
http://guides.rubyonrails.org/v2.3.11/testing.html

Github lifo/docrails History:
https://github.com/rails/rails/commits/ff359af86505b4d317b7467e7f79aa2ef2c5e795/railties/doc/guides/source/testing_rails_applications.txt
Move view_paths from AP to AV
Require only path_set && lookup_context instead of whole base
Move rendering from AP to AV
Add loading 'action_view' as part of rails/all
Move layouts to AV
Hook up AV::Rendering on AV intialization
Revert "Require only path_set && lookup_context instead of whole base"

This reverts commit 77bb03df2ca3687b290e9fe77d21007642f0329c.
Fix AV tests, I18nProxy was moved to AV
Fix eager_autoload for layouts

Name was singular, should be plural
Integrate ActionMailer with ActionView
Do not include AV::Rendering

It's already included in Layouts, makes no sense to doubly include it
Fix AP test suite after moving stuff to AV
Rename abstract_controller/rendering. to errors.rb

Since all rendering stuff was extracted to AV, the only thing that left was single class with error so file name wasn't relevant anymore
Revert "Rename abstract_controller/rendering. to errors.rb"

This reverts commit 6fe91ec5008838338e54ab8570f7c95ee0cdd8e8.
Create AbstractController::Rendering interface

This interface should be use when implementing renderers.
Remove 'api plugin' from docs

AbstractController::Rendering is module which defines thie api
No need for .rb extension