Added generic typing to jQuery.when

jquery/jquery-tests.ts

@@ -2294,4 +2294,8 @@ function test_EventIsNewable() {
 
 function test_EventIsCallable() {
     var ev = jQuery.Event('click');
-}
+}
+
+var f1: JQueryPromise<string> = $.when("fetch");
+var f2: JQueryPromise<string[]> = f1.then(s => [s, s]);
+var f3: JQueryPromise<number> = f2.then(v => 3);

jquery/jquery.d.ts

@@ -265,7 +265,7 @@ interface JQueryStatic {
 
     noConflict(removeAll?: boolean): Object;
 
-    when(...deferreds: any[]): JQueryPromise;
+    when<T>(...deferreds: T[]): JQueryPromise<T>;
 
     // CSS
     css(e: any, propertyName: string, value?: any);