Refactored AbstractController to provide better hook points for overriding aspects of action dispatching

Conflicts:
	actionpack/lib/action_view/helpers/form_helper.rb

Signed-off-by: NMichael Koziarski <michael@koziarski.com>

Conflicts:
	actionpack/lib/action_controller/abstract/base.rb
	actionpack/lib/action_controller/routing.rb

Got new base to pass controller/base_test.rb, implemented method_missing action semantics in compatibility mode, and fixed a few action_missing bugs.

Changed ActiveRecord::Base#exists? to invoke find_initial so that it is compatible with, and doesn't lose, :include scopes (references to eager loaded tables)
Signed-off-by: NMichael Koziarski <michael@koziarski.com>
[#2543 state:committed]

Conflicts:
	actionpack/lib/action_controller/abstract/callbacks.rb
	actionpack/lib/action_controller/abstract/renderer.rb
	actionpack/lib/action_controller/base/base.rb
	actionpack/lib/action_controller/dispatch/dispatcher.rb
	actionpack/lib/action_controller/routing/route_set.rb
	actionpack/lib/action_controller/testing/process.rb
	actionpack/test/abstract_controller/layouts_test.rb
	actionpack/test/controller/filters_test.rb
	actionpack/test/controller/helper_test.rb
	actionpack/test/controller/render_test.rb
	actionpack/test/new_base/test_helper.rb

This reverts commit a747ab5b.

[#2594 state:open]

This reverts commit 99c103be.