Merge rev 27695 from 3.3 branch.

Transaction.begin().

When raising DeprecationWarning, point the warning machinery at
the caller, not at Transaction.begin() itself.  As is (voice
of experience <wink>), these warnings are darned near useless to
track down code that needs to be changed on Zope trunk.  With the
change, the warnings point directly at the deprecated uses.

NEWS.txt

@@ -25,6 +25,12 @@ ZODB/component.xml
 type ``byte-size``.  This allows you to specify, for example,
 "``cache-size 20MB``" to get a 20 megabyte cache.
 
+transaction
+-----------
+
+The deprecation warning for ``Transaction.begin()`` was changed to
+point to the caller, instead of to ``Transaction.begin()`` itself.
+
 
 What's new in ZODB3 3.3 release candidate 1?
 ============================================

src/transaction/_transaction.py

@@ -263,7 +263,7 @@ class Transaction(object):
     def begin(self):
         warnings.warn("Transaction.begin() should no longer be used; use "
                       "the begin() method of a transaction manager.",
-                      DeprecationWarning)
+                      DeprecationWarning, stacklevel=2)
         if (self._resources or
               self._sub or
               self._nonsub or