Merged the queryset-refactor branch into trunk.

This is a big internal change, but mostly backwards compatible with existing
code. Also adds a couple of new features.

Fixed #245, #1050, #1656, #1801, #2076, #2091, #2150, #2253, #2306, #2400, #2430, #2482, #2496, #2676, #2737, #2874, #2902, #2939, #3037, #3141, #3288, #3440, #3592, #3739, #4088, #4260, #4289, #4306, #4358, #4464, #4510, #4858, #5012, #5020, #5261, #5295, #5321, #5324, #5325, #5555, #5707, #5796, #5817, #5987, #6018, #6074, #6088, #6154, #6177, #6180, #6203, #6658


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7477 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/modeltests/basic/models.py

@@ -292,11 +292,9 @@ datetime.datetime(2005, 7, 28, 0, 0)
 >>> Article.objects.all()[2:][2:3]
 [<Article: Default headline>]
 
-# Note that you can't use 'offset' without 'limit' (on some dbs), so this doesn't work:
->>> Article.objects.all()[2:]
-Traceback (most recent call last):
-    ...
-AssertionError: 'offset' is not allowed without 'limit'
+# Using an offset without a limit is also possible.
+>>> Article.objects.all()[5:]
+[<Article: Fourth article>, <Article: Article 7>, <Article: Updated article 8>]
 
 # Also, once you have sliced you can't filter, re-order or combine
 >>> Article.objects.all()[0:5].filter(id=1)