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/expressions_regress/models.py

@@ -2,7 +2,7 @@
 Spanning tests for all the operations that F() expressions can perform.
 """
 from django.conf import settings
-from django.db import models
+from django.db import models, DEFAULT_DB_ALIAS
 
 #
 # Model for testing arithmetic expressions.
@@ -121,7 +121,7 @@ Complex expressions of different connection types are possible.
 """}
 
 # Oracle doesn't support the Bitwise OR operator.
-if settings.DATABASE_ENGINE != 'oracle':
+if settings.DATABASES[DEFAULT_DB_ALIAS]['ENGINE'] != 'django.db.backends.oracle':
     __test__['API_TESTS'] += """
 
 >>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)