Auditing the audit function

"My organization just underwent our 2015 transition audit by an external registrar. Prior to the external audit, a full system audit was conducted by internal auditors and documented. However, much attention was focused on whether the internal audit function as under 9.2 was audited internally. To me, it appears that 9.2 requires that a full internal audit of the management system is conducted prior to certification. But, does 9.2 require that the internal audit function (9.2) is also audited by a separate group of independent auditors prior to certification? We were advised that if the internal audit had not been audited prior to a registrar audit, then this is considered as a non-conformity, because the entire 14001 standard would have not been satisfied. Can you provide clarity on the intent of 9.2?”