Repair code trying to start a new transaction.

Never do these in ZODB 3:3:

    get_transaction().begin()
    some_txn_object.begin()

They raise DeprecationWarning, and don't do exactly what they
did in ZODB 3.2.  Instead do:

    import transaction

and then one of these:

    transaction.begin()
    new_txn_object = transaction.begin()

zopepublication.py

@@ -22,6 +22,7 @@
 from new import instancemethod
 
 from ZODB.POSException import ConflictError
+import transaction
 
 from zope.event import notify
 from zope.security.interfaces import Unauthorized
@@ -77,7 +78,7 @@ def beforeTraversal(self, request):
 
         request.setPrincipal(p)
         newInteraction(request)
-        get_transaction().begin()
+        transaction.begin()
 
     def _maybePlacefullyAuthenticate(self, request, ob):
         if not IUnauthenticatedPrincipal.providedBy(request.principal):
@@ -346,8 +347,7 @@ def handleException(self, object, request, exc_info, retry_allowed=True):
                     get_transaction().abort()
 
     def beginErrorHandlingTransaction(self, request, ob, note):
-        txn = get_transaction()
-        txn.begin()
+        txn = transaction.begin()
         txn.note(note)
         self.annotateTransaction(txn, request, ob)
         return txn