构造函数//JavaScript.System.Net.HttpRequest = function()
//JavaScript.System.Net.HttpRequest = function(url)
//JavaScript.System.Net.HttpRequest = function(usepost)
//JavaScript.System.Net.HttpRequest = function(onresponse)
//JavaScript.System.Net.HttpRequest = function(url, usepost)
//JavaScript.System.Net.HttpRequest = function(url, onresponse)
//JavaScript.System.Net.HttpRequest = function(usepost, async)
//JavaScript.System.Net.HttpRequest = function(onresponse, async)
//JavaScript.System.Net.HttpRequest = function(user, password)
//JavaScript.System.Net.HttpRequest = function(url, usepost, onresponse)
//JavaScript.System.Net.HttpRequest = function(url, usepost, async)
//JavaScript.System.Net.HttpRequest = function(url, onresponse, async)
//JavaScript.System.Net.HttpRequest = function(url, user, password)
//JavaScript.System.Net.HttpRequest = function(usepost, onresponse, async)
//JavaScript.System.Net.HttpRequest = function(usepost, user, password)
//JavaScript.System.Net.HttpRequest = function(onresponse, user, password)
//JavaScript.System.Net.HttpRequest = function(url, usepost, onresponse, async)
//JavaScript.System.Net.HttpRequest = function(url, usepost, user, password)
//JavaScript.System.Net.HttpRequest = function(url, onresponse, user, password)
//JavaScript.System.Net.HttpRequest = function(usepost, onresponse, user, password)
//JavaScript.System.Net.HttpRequest = function(usepost, async, user, password)
//JavaScript.System.Net.HttpRequest = function(onresponse, async, user, password)
//JavaScript.System.Net.HttpRequest = function(url, usepost, onresponse, user, password)
//JavaScript.System.Net.HttpRequest = function(url, usepost, async, user, password)
//JavaScript.System.Net.HttpRequest = function(url, onresponse, async, user, password)
//JavaScript.System.Net.HttpRequest = function(usepost, onresponse, async, user, password)
//JavaScript.System.Net.HttpRequest = function(url, usepost, onresponse, async, user, password)方法:    this.SetUrl = this.set_Url = function(value)
    this.SetUsePost = this.set_UsePost = function(value)
    this.SetIsAsync = this.set_IsAsync = function(value)
    this.SetUserName = this.set_UserName = function(value)
    this.SetPassword = this.set_Password = function(value)
    this.SetRequestHeader = this.setRequestHeader = function(name, value)
    this.RemoveRequestHeader = this.removeRequestHeader = function(name)
    this.GetRequestHeader = this.getRequestHeader = function(name)
    this.GetRequestHeaders = this.getRequestHeaders = 
    this.GetAllRequestHeaders = this.getAllRequestHeaders = function()
    this.GetResponseHeader = this.getResponseHeader = function(name)
    this.GetResponseHeaders = this.getResponseHeaders = 
    this.GetAllResponseHeaders = this.getAllResponseHeaders = function()
    this.SetContentType = this.set_ContentType = function(value)
    this.SetFailedAction = this.set_FailedAction = function(value)
    this.IsResponseSuccess = this.isResponseSuccess = function()
    this.SetData = this.set_Data = function(value)事件:
      onopen                    当正在打开一个 HTTP 请求时发生
      onreadystatechange        当 HTTP 请求的准备状态发生改变时发生
      onresponse                当 HTTP 请求成功响应时发生
      onfail                    当 HTTP 请求成功响应后被检测到 HTTP 请求失败时发生
      onsuccess                 当 HTTP 请求成功响应后被检测到 HTTP 请求成功时发生
      onerror                   当运行错误时发生