AthenaPoolCnvSvc: Pass SG key to createPersistent/createTransient.
Rename T_AthenaPoolCustomCnv to T_AthenaPoolCustomCnvWithKey, changing the interfaces for the create methods to pass through the SG key. For compatibility, create T_AthenaPoolCustomCnv deriving from it with the old interfaces.
Update T_AthenaPoolxAODCnv and T_AthenaPoolAuxContainerCnv to use this. In the process, we can remove the xAODCnv hack where we override createObj() in order to get the SG key. (This turns out to be a race; see ATEAM-567.)
A couple other minor cleanups.
Edited by Scott Snyder