Intercept and customize error from Guzzle

When guzzle is initalized it tried to find a suitable handler to use. If no handler can be found (for example curl)
an exception is thrown.
With this change we try to find the handler before creating the client so we can pass the handler to the client manually.
Doing this, we are able to customize the error message to make it (potentially) less confusing for the users
who might have no idea what guzzle is.

Author: Emil Andersson

src/Symfony/Installer/DownloadCommand.php

@@ -19,6 +19,7 @@
 use GuzzleHttp\Client;
 use GuzzleHttp\Exception\ClientException;
 use GuzzleHttp\Event\ProgressEvent;
+use GuzzleHttp\Utils;
 use Symfony\Component\Console\Command\Command;
 use Symfony\Component\Console\Helper\ProgressBar;
 use Symfony\Component\Console\Input\InputInterface;
@@ -221,7 +222,15 @@ protected function getGuzzleClient()
             $defaults['debug'] = true;
         }
 
-        return new Client(array('defaults' => $defaults));
+        try {
+            $handler = Utils::getDefaultHandler();
+        } catch (\RuntimeException $e) {
+            throw new \RuntimeException(
+                'The Symfony installer requires the php-curl extension or the '
+                .'allow_url_fopen ini setting.');
+        }
+
+        return new Client(array('defaults' => $defaults, 'handler' => $handler));
     }
 
     /**