[Futures] accept/resolve/reject on a resolver don't have clearly defined behavior if no value is passed

The spec has:

   void accept(optional any value);

and the prose says:

   The accept(value) method must run context object's accept with value.

But "value" is optional, so it can be not passed.  And the accept 
algorithm assumes there is a value.  Maybe.  It certainly passes the 
value to callbacks, but those callbacks have an _optional_ argument.  So 
maybe the intent is that if accept() is not passed a value the callbacks 
will also not be passed a value?

This needs to be clarified.

-Boris