Fixed typo one line in layouts and rendering: stylesheet_link_tag for file in subdirectory.

* Fix one error
* Improve wording
* Improve punctuation

New exceptions pages for development

[ci skip]

Updated copyright notices for 2013

refatctoring of some code repetition in spawn_methods

This reverts commit 9c18b6a8.

Fix usage of lambda as a Rack endpoint

These tests are needed only if we are using MiniTest::Spec

minitest/autorun load minitest/spec polluting the global namespace with
the DSL that we don't want on Rails

This reverts commit 22bc12ec.

REASON: We will remove the MiniTest::Spec from Rails and we need these
methods again

Conflicts:
	activesupport/lib/active_support/test_case.rb

The response body needs to respond_to? :each.

Charset should not be appended to image/* type

      1) Failure:
    test_head_created_with_image_png_content_type(RenderTest) [test/controller/render_test.rb:1238]:
    Expected: "image/png"
      Actual: "image/png; charset=utf-8"

Rack::Lock actually sets rack.multithread to `false`, not `true`.

Presumably because once inside the mutex, the app can function as if it were single threaded.

Define [], []=, permanent, signed and encrypted as the only allowed methods for the non Raw Cookie classes

fix testcase: ruby-2.0.0 warned unused variables