Add promise to JQueryDeferred

Add promise method returning JQueryPromise from JQueryDeferred:
http://api.jquery.com/deferred.promise/

jquery/jquery.d.ts

@@ -104,6 +104,7 @@ interface JQueryDeferred extends JQueryPromise {
     resolveWith(context: any, ...args: any[]): JQueryDeferred;
     state(): string;
     then(doneCallbacks: any, failCallbacks?: any, progressCallbacks?: any): JQueryDeferred;
+    promise(target?: any): JQueryPromise;
 }
 
 /*