fix code that figures out if the asset pipeline is enabled

The Rails3-compatible algorithm to figure out if the asset pipeline is
doesn't work with Rails4.  Quite frankly, the new one doesn't seem as
clean as the old one, but hopefully this code will work in all cases.

rails/rails#10334

Note that the specs didn't seem to test both cases, or else the image
path is now the same whether the pipeline is enabled or not, but in
any case the specs don't need to determine whether the pipeline is
enabled, they can use the same path in all cases.

lib/surveyor/helpers/asset_pipeline.rb

@@ -4,9 +4,14 @@ module AssetPipeline
       ##
       # Returns whether or not the asset pipeline is present and enabled.
       #
-      # The detection scheme used here was ripped from jquery-rails.
+      # With Rails4 it appears that assets.enabled is false if
+      # --skip-sprockets is specified when creating the application,
+      # but the assets.enabled option is nil in the default case
+      # (i.e., pipeline enabled).
       def asset_pipeline_enabled?
-        ::Rails.version >= "3.1" && ::Rails.application.config.assets.enabled
+        return false unless Rails.configuration.respond_to?('assets')
+        assets = Rails.configuration.assets
+        assets.enabled.nil? || assets.enabled
       end
     end
   end

spec/helpers/surveyor_helper_spec.rb

@@ -2,7 +2,6 @@
 
 describe SurveyorHelper do
   context "numbering" do
-    let(:asset_directory){ asset_pipeline_enabled? ? "assets" : "images" }
     before do
       ActionController::Base.helpers.config.assets_dir = "public" unless asset_pipeline_enabled?
     end
@@ -15,7 +14,7 @@
       helper.q_text(q1).should == "<span class='qnum'>1) </span>#{q1.text}"
       helper.q_text(q2).should == q2.text
       helper.q_text(q3).should == q3.text
-      helper.q_text(q4).should == %Q(<img alt="Something" src="/#{asset_directory}/something.jpg" />)
+      helper.q_text(q4).should == %Q(<img alt="Something" src="/images/something.jpg" />)
       helper.q_text(q5).should == q5.text
     end
   end
@@ -115,4 +114,4 @@ def rc_to_as(type_sym)
       helper.rc_to_as(:date).should == :string      # back to string
     end
   end
-end
+end

spec/models/answer_spec.rb

@@ -124,14 +124,13 @@
   end
 
   context "for views" do
-    let(:asset_directory){ asset_pipeline_enabled? ? "assets" : "images" }
     before do
       ActionController::Base.helpers.config.assets_dir = "public" unless asset_pipeline_enabled?
     end
     it "#text_for with #display_type == image" do
       answer.text = "rails.png"
       answer.display_type = :image
-      answer.text_for.should == %(<img alt="Rails" src="/#{asset_directory}/rails.png" />)
+      answer.text_for.should == %(<img alt="Rails" src="/images/rails.png" />)
     end
     it "#text_for with #display_type == hidden_label" do
       answer.text = "Red"
@@ -172,4 +171,4 @@
       answer.text_for(:post).should == "after|extra"
     end
   end
-end
+end

spec/models/question_spec.rb

@@ -172,14 +172,13 @@
   end
 
   context "for views" do
-    let(:asset_directory){ asset_pipeline_enabled? ? "assets" : "images" }
     before do
       ActionController::Base.helpers.config.assets_dir = "public" unless asset_pipeline_enabled?
     end
     it "#text_for with #display_type == image" do
       question.text = "rails.png"
       question.display_type = :image
-      question.text_for.should == %(<img alt="Rails" src="/#{asset_directory}/rails.png" />)
+      question.text_for.should == %(<img alt="Rails" src="/images/rails.png" />)
     end
     it "#help_text_for"
     it "#text_for preserves strings" do