1.添加一个SetHeaderValue方法：
public static void SetHeaderValue(WebHeaderCollection header, string name, string value)
{
var property = typeof(WebHeaderCollection).GetProperty("InnerCollection",BindingFlags.Instance | BindingFlags.NonPublic);
if (property != null)
{
var collection = property.GetValue(header, null) as NameValueCollection;
collection[name] = value;
}
}
public static voi
