defer warnings/exceptions of the client

This enables the following pattern:

<?php
use http\Client;

function handle_response_and_dequeue($res) {
	var_dump($res->getResponseCode());
	return true; //dequeue
}

$client = new Client;
$client->enqueue(new Client\Request(...),"handle_response_and_dequeue");
$client->enqueue(new Client\Request(...),"handle_response_and_dequeue");
$client->enqueue(new Client\Request(...),"handle_response_and_dequeue");

while (count($client)) {
	try {
		$client->send();
	} catch (Exception $e) {
		echo $e->getMessage(),"\n";
	}
}