Fix bug in class used by OAI Harvest

The original method used was just detecting when a record was found via the close tag, which resulted in the occasional corruption of raw-records due to the OAI-PMH harvest data being included.  Improved but not foolproof method waits for opening tag to be hit before writing to the buffer that generates the record.   I have not tested this with multiple tags to split on.  That situation would complicate the harvest especially if the tags were nested inside each other.