Send ETag header with 304 response as well

spec/directories_spec.rb

@@ -80,6 +80,7 @@ describe "Directories" do
 
         last_response.status.must_equal 304
         last_response.body.must_be_empty
+        last_response.headers["ETag"].must_equal @etag
       end
 
       it "responds normally when it does not match the current ETag" do

spec/riak_spec.rb

@@ -89,6 +89,7 @@ describe "App with Riak backend" do
 
           last_response.status.must_equal 304
           last_response.body.must_be_empty
+          last_response.headers["ETag"].must_equal @etag
         end
 
         it "responds normally when it does not match the current ETag" do