Fix the issue that a normal transaction in RDBI may be held off by an "auto-select" transaction

[samwang]

In the RDBI framework, transactions are ended strictly due to their nesting order. However, there are situations that between calling tran_begin and trans_end(for non query operations), a query is executed. This causes the non-query transaction not the top on transaction start, thus will fail to end. This ticket aims at fixing this problem by skipping transactions with ids which start with "auto-exec-" when trying to find a matching transaction to end.