Expose XHR instance

Fixes gh-64

lib/adapters/http.js

@@ -106,7 +106,8 @@ module.exports = function httpAdapter(resolve, reject, config) {
         status: res.statusCode,
         statusText: res.statusMessage,
         headers: res.headers,
-        config: config
+        config: config,
+        request: req
       };
 
       // Resolve or reject the Promise based on the status

lib/adapters/xhr.js

@@ -68,7 +68,8 @@ module.exports = function xhrAdapter(resolve, reject, config) {
       status: request.status === 1223 ? 204 : request.status,
       statusText: request.status === 1223 ? 'No Content' : request.statusText,
       headers: responseHeaders,
-      config: config
+      config: config,
+      request: request
     };
 
     // Resolve or reject the Promise based on the status