Support for multiple payment processors - need to update api

As part of the work done on supporting multiple payment processors we need to ensure that the api still works in 4.2 as it did in 4.1

• ie.

civicrm_api('event','create',array('id'=> 1, 'payment_processor_id' =>1);

should not be broken by the MIH changes - I'm less concerned about the get action as I can't think of a lot of use cases where it would be important