This macro is arguably too clever by half.  I'm not even sure how it gets evaluated.

`NanAssignPersistent(persistent, handle_)` gets transformed into `_NAN_GET_MACRO32(persistent, handle_, _NanAssignPersistentOldHelper, _NanAssignPersistentNewHelper)` which then becomes `_NanAssignPersistentNewHelper(persistent, handle_)`?