rescue_from handlers are not being honored in functional tests

rescue_from handlers are not being honored in functional tests since commit 90c930f45c5c6766306929241462ffff8f67b86e.

Consider the following trivial controller and test, from a rails application created with the current edge code:

class ThingsController < ApplicationController
  rescue_from ActiveRecord::RecordNotFound, :with => :record_not_found

  def show
    @thing = Thing.find(params[:id])
  end

  # ...

  private
  def record_not_found
    flash[:error] = 'That thing could not be found'
    redirect_to things_url
  end
end

require 'test_helper'

class ThingsControllerTest < ActionController::TestCase
  test "show with invalid id should set flash and redirect" do
    get :show, :id => nil
    assert_equal 'That thing could not be found', flash[:error]
    assert_redirected_to things_url
  end
end

This functional test should pass because rescue_from should handle the ActiveRecord::RecordNotFound exception raised by Thing.find(nil). Instead, the exception falls through to the test, which aborts before hitting the assertions:

  1) Error:
test_show_with_invalid_id_should_set_flash_and_redirect(ThingsControllerTest):
ActiveRecord::RecordNotFound: Couldn't find Thing without an ID

The attached patch reverts a removal of rescue_action_with_handler that happened in commit 90c930f45c5c6766306929241462ffff8f67b86e. With this patch, the above test passes. However, I am not sure that this patch is the correct solution.