/posts/:id/events: list is_resolved correctly for appeals.

/posts/:id/events incorrectly lists appeals as always being resolved.
This is because events UNION together appeals and flags, which doesn't
quite work because for appeals is_resolved is a method, not an
attribute. is_resolved was hardcoded to true so it'd work in the UNION.

This changes PostEvent to be a wrapper object around PostFlag /
PostAppeal, instead of a UNION. PostEvent delegates everything to the
inner flag/appeals object, so that is_resolved works correctly.

Also, this incidentally fixes a problem with /posts/:id/event.xml not
serializing correctly.

test/functional/post_events_controller_test.rb

@@ -26,4 +26,21 @@ class PostEventsControllerTest < ActionController::TestCase
       assert_response :ok      
     end
   end
+
+  context "GET /posts/:post_id/events.xml" do
+    setup do
+      get :index, {:post_id => @post.id, :format => :xml}, {:user_id => CurrentUser.user.id}
+
+      @xml = Hash.from_xml(response.body)
+      @appeal = @xml["post_events"].find { |e| e["type"] == "a" }
+    end
+
+    should "render" do
+      assert_not_nil(@appeal)
+    end
+
+    should "return is_resolved correctly" do
+      assert_equal(false, @appeal["is_resolved"])
+    end
+  end
 end