Fix user subobject problems resulting from getting the iterator for the

class prototype...

Solution from
https://developer.mozilla.org/en/SpiderMonkey/JSAPI_Reference/JS_InitClass

Note: By default JS_InitClass creates a prototype object but does not invoke
the constructor (JSClass.construct) on it. However, the prototype object
will eventually be finalized (JSClass.finalize). This inconsistency can
cause problems; for example, if the finalizer calls JS_GetPrivate(),
expecting that the constructor called JS_SetPrivate(), it may find that the
private data is NULL. The JSCLASS_CONSTRUCT_PROTOTYPE flag is one way to
avoid this inconsistency.