RFC2616 When sending a request through a proxy URI must be in an abso…

…luteURI format. Fixes #10038

src/Http/Client/Adapter/Stream.php

@@ -202,6 +202,7 @@ protected function _buildOptions(Request $request, $options)
             $this->_contextOptions['max_redirects'] = (int)$options['redirect'];
         }
         if (isset($options['proxy']['proxy'])) {
+            $this->_contextOptions['request_fulluri'] = true;
             $this->_contextOptions['proxy'] = $options['proxy']['proxy'];
         }
     }