Reorganize loader for compass support

::Sprockets is the wrong check, since we reference the ::Rails constant directly in the loaded file. This was outright failing when used with an empty compass-sprockets-sass install (without Rails)

lib/bootstrap-sass.rb

@@ -3,20 +3,22 @@ module Bootstrap
 
   # Inspired by Kaminari
   def self.load!
-    if compass? && asset_pipeline?
-      register_compass_extension
-      register_rails_engine
-    elsif compass?
-      # Only require compass extension if a standalone project
+    if compass?
       require 'bootstrap-sass/compass_functions'
       register_compass_extension
     elsif asset_pipeline?
-      require 'sass-rails' # See: https://github.com/thomas-mcdonald/bootstrap-sass/pull/4
+      require 'bootstrap-sass/sass_functions'
+    end
+
+    if rails?
+      require 'sass-rails'
       register_rails_engine
-      require 'bootstrap-sass/rails_functions'
-    else
+    end
+
+    if !(rails? || compass?)
       raise Bootstrap::FrameworkNotFound, "bootstrap-sass requires either Rails > 3.1 or Compass, neither of which are loaded"
     end
+    
     stylesheets = File.expand_path(File.join("..", 'vendor', 'assets', 'stylesheets'))
     ::Sass.load_paths << stylesheets
   end
@@ -30,6 +32,10 @@ module Bootstrap
     defined?(::Compass)
   end
 
+  def self.rails?
+    defined?(::Rails)
+  end
+
   def self.register_compass_extension
     base = File.join(File.dirname(__FILE__), '..')
     styles = File.join(base, 'vendor', 'assets', 'stylesheets')