domain preserve error since release 2.9.31

[rain1017]

Test code. error since release 2.9.31

var P = require('bluebird');
var domain = require('domain');

P.each([1], function(){
    var d = domain.create();
    d.run(function(){
        P.each([1], function(){
            if(!process.domain){
                throw new Error('domain error!');
            }
        });
    });
});