Tests for transactional undo support need to be more cautious:

If a storage doesn't support T.U. and is old enough, you need to first
check if it has a supportsTransactionalUndo attribute.

trunk/src/ZODB/tests/VersionStorage.py

@@ -169,7 +169,8 @@ class VersionStorage:
         #JF#                   'bogus', self._transaction)
 
         # And try to abort the empty version
-        if self._storage.supportsTransactionalUndo():
+        if (hasattr(self._storage, 'supportsTransactionalUndo')
+            and self._storage.supportsTransactionalUndo()):
             # XXX FileStorage used to be broken on this one
             self.assertRaises(POSException.VersionError,
                               self._storage.abortVersion,
@@ -185,7 +186,8 @@ class VersionStorage:
         eq(zodb_unpickle(data), MinPO(51))
 
     def checkCommitVersionErrors(self):
-        if not self._storage.supportsTransactionalUndo():
+        if not (hasattr(self._storage, 'supportsTransactionalUndo')
+            and self._storage.supportsTransactionalUndo()):
             # XXX FileStorage used to be broken on this one
             return
         eq = self.assertEqual