Collector 1860: use an optimistic savepoint in CopySupport._getCopy

(there's no possiblity of rollback here, so no need to insist that the
data manager support rollbacks).

The other part of this change is in ZODB 3.4.1b4, also stitched in
by this checkin.

lib/python/OFS/CopySupport.py

@@ -461,7 +461,7 @@ class CopySource(ExtensionClass.Base):
         # 1) Make sure the data about to be exported is current
         # 2) Ensure self._p_jar and container._p_jar are set even if
         #    either one is a new object
-        transaction.savepoint()
+        transaction.savepoint(optimistic=True)
 
         if self._p_jar is None:
             raise CopyError, (