Deprecated TransactionMiddleware and TRANSACTIONS_MANAGED.

Replaced them with per-database options, for proper multi-db support.

Also toned down the recommendation to tie transactions to HTTP requests.
Thanks Jeremy for sharing his experience.

tests/handlers/views.py

@@ -0,0 +1,17 @@
+from __future__ import unicode_literals
+
+from django.db import connection
+from django.http import HttpResponse, StreamingHttpResponse
+
+def regular(request):
+    return HttpResponse(b"regular content")
+
+def streaming(request):
+    return StreamingHttpResponse([b"streaming", b" ", b"content"])
+
+def in_transaction(request):
+    return HttpResponse(str(connection.in_atomic_block))
+
+def not_in_transaction(request):
+    return HttpResponse(str(connection.in_atomic_block))
+not_in_transaction.transactions_per_request = False