Fixed #5791 -- Added early-bailout support for views (ETags and Last-modified).

This provides support for views that can have their ETag and/or Last-modified
values computed much more quickly than the view itself. Supports all HTTP
verbs (not just GET).

Documentation and tests need a little more fleshing out (I'm not happy with the
documentation at the moment, since it's a bit backwards), but the functionality
is correct.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10114 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/conditional_processing/urls.py

@@ -0,0 +1,8 @@
+from django.conf.urls.defaults import *
+import views
+
+urlpatterns = patterns('',
+    ('^$', views.index),
+    ('^last_modified/$', views.last_modified),
+    ('^etag/$', views.etag),
+)