Fixed #1142 -- Added multiple database support.

This monster of a patch is the result of Alex Gaynor's 2009 Google Summer of Code project.
Congratulations to Alex for a job well done.

Big thanks also go to:
 * Justin Bronn for keeping GIS in line with the changes,
 * Karen Tracey and Jani Tiainen for their help testing Oracle support
 * Brett Hoerner, Jon Loyens, and Craig Kimmerer for their feedback.
 * Malcolm Treddinick for his guidance during the GSoC submission process.
 * Simon Willison for driving the original design process
 * Cal Henderson for complaining about ponies he wanted.

... and everyone else too numerous to mention that helped to bring this feature into fruition.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11952 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/model_inheritance_regress/models.py

@@ -314,7 +314,8 @@ DoesNotExist: ArticleWithAuthor matching query does not exist.
 # likely to ocurr naturally with model inheritance, so we check it here).
 # Regression test for #9390. This necessarily pokes at the SQL string for the
 # query, since the duplicate problems are only apparent at that late stage.
->>> sql = ArticleWithAuthor.objects.order_by('pub_date', 'pk').query.as_sql()[0]
+>>> qs = ArticleWithAuthor.objects.order_by('pub_date', 'pk')
+>>> sql = qs.query.get_compiler(qs.db).as_sql()[0]
 >>> fragment = sql[sql.find('ORDER BY'):]
 >>> pos = fragment.find('pub_date')
 >>> fragment.find('pub_date', pos + 1) == -1