Fix undo error detection code.

Undo fails if any of the following is true:
- cell_list is empty (should never happen, add an assertion for this)
- all connections get a ConnectionClosed exception
- transaction cannot be found in any storage
- an unexpected answer was received (it did not change txn_info)

This fixes the first case, as the test might have received old values from
former executions (which could be neither -1 nor 0) in the same
transaction.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1832 71dcc9de-d417-0410-9af5-da40c76e7ee4

neo/client/app.py

@@ -765,6 +765,8 @@ class Application(object):
 
         # First get transaction information from a storage node.
         cell_list = self._getCellListForTID(transaction_id, readable=True)
+        assert len(cell_list), 'No cell found for transaction %s' % (
+            dump(tid), )
         shuffle(cell_list)
         for cell in cell_list:
             conn = self.cp.getConnForCell(cell)
@@ -787,8 +789,7 @@ class Application(object):
                 break
             else:
                 raise NEOStorageError('undo failed')
-
-        if self.local_var.txn_info in (-1, 0):
+        else:
             raise NEOStorageError('undo failed')
 
         oid_list = self.local_var.txn_info['oids']