HTTP API: Fix compatibility with cURL <7.22

Ensure connections are closed after usage to fix an issue with WP.com URLs used in the tests.

Resynched from GitHub at 95518ce.

See #33055.

Built from https://develop.svn.wordpress.org/trunk@37430


git-svn-id: http://core.svn.wordpress.org/trunk@37396 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/Requests/Transport/cURL.php

@@ -309,6 +309,11 @@ class Requests_Transport_cURL implements Requests_Transport {
 	protected function setup_handle($url, $headers, $data, $options) {
 		$options['hooks']->dispatch('curl.before_request', array(&$this->handle));
 
+		// Force closing the connection for old versions of cURL (<7.22).
+		if ( ! isset( $headers['Connection'] ) ) {
+			$headers['Connection'] = 'close';
+		}
+
 		$headers = Requests::flatten($headers);
 
 		if (!empty($data)) {