从ASINetWorkQueue中删除所有请求

- (void)fillAndRunQueue:(ASINetworkQueue*)queue requests:(NSArray*)requests {  
    for (ASIHTTPRequest* request in requests) {  
        if ([request check]) { // Valid request => add it to the queue    
            [queue addOperation:request];  
        } else { // Invalid request => cancel immediatelly  
            // HOW TO REMOVE ALL PREVIOUS REQUESTS FROM THE QUEUE??  
            return;  
        }  
    }  

    [queue go];  
}