Fixed #24143 -- Encouraged use of Http404 messages for debugging.

docs/topics/http/shortcuts.txt

@@ -313,7 +313,7 @@ This example is equivalent to::
         try:
             my_object = MyModel.objects.get(pk=1)
         except MyModel.DoesNotExist:
-            raise Http404
+            raise Http404("No MyModel matches the given query.")
 
 The most common use case is to pass a :class:`~django.db.models.Model`, as
 shown above. However, you can also pass a
@@ -383,4 +383,4 @@ This example is equivalent to::
     def my_view(request):
         my_objects = list(MyModel.objects.filter(published=True))
         if not my_objects:
-            raise Http404
+            raise Http404("No MyModel matches the given query.")

docs/topics/http/views.txt

@@ -119,13 +119,18 @@ Example usage::
         try:
             p = Poll.objects.get(pk=poll_id)
         except Poll.DoesNotExist:
-            raise Http404
+            raise Http404("Poll does not exist")
         return render_to_response('polls/detail.html', {'poll': p})
 
 In order to use the ``Http404`` exception to its fullest, you should create a
 template that is displayed when a 404 error is raised. This template should be
 called ``404.html`` and located in the top level of your template tree.
 
+If you provide a message when raising an ``Http404`` exception, it will appear
+in the standard 404 template displayed when :setting:`DEBUG` is ``True``. Use
+these messages for debugging purposes; they generally aren't suitable for use
+in a production 404 template.
+
 .. _customizing-error-views:
 
 Customizing error views