Plug the memory leak from gss_OID_set_sap_to_loc

Make the (one) caller free what it allocates, but don't try to free
NULL OID_sets.
Plug the memory leak from gss_OID_set_loc_to_sap

This is used when the GSS-API library allocates storage for returning
to the application, but that structure is in the wrong ABI.  We translate
it, allocating our own storage, but must release the library-allocated
storage at this time, as no other references to it will exist.
Plug the memory leak from gss_OID_sap_to_loc

This routine is only used to translate data coming from SAP through
the SNC Adapter into the ABI used by the local GSS-API library.
As such, the output of the routine is never exposed outside of the
shim layer, so we can make all callers (in the shim layer) free its
output, closing the memory leak.  (But don't try to free a NULL OID.)