在iOS7中，内购只能在真机上才会调用
- (void)productsRequest:(SKProductsRequest *)request didReceiveResponse:(SKProductsResponse *)response协议方法
若是用模拟器，它回调用
- (void)request:(SKRequest *)request didFailWithError:(NSError *)error
{
DLog(@"error ====== %@", error);
}
log:
error ====== Error Domain=SSErrorDomain Code=2 "无法连接到 iTunes Store" UserInfo=0xb56aaa0 {NSLocalizedDescription=无法连接到 iTunes Store}