创建命名空间

function createNamespace(name){
	var domains = name.split('.');
	var cur_domain = window;
	for(var i=0,len=domains.length;i<len;i++){
		var domain = domains[i];
		if(typeof cur_domain[domain] == 'undefined'){
			cur_domain[domain] = {};
		}
		cur_domain = cur_domain[domain]
	}
	return cur_domain;
}