feat(ng_for): Add Even and Odd variables to ng_for

Add even and odd local variables to ng_for to allow developers to style table rows differently and other features.

Closes #4181

modules/angular2/src/core/directives/ng_for.ts

@@ -90,6 +90,8 @@ export class NgFor implements DoCheck {
   private _perViewChange(view, record) {
     view.setLocal('\$implicit', record.item);
     view.setLocal('index', record.currentIndex);
+    view.setLocal('even', (record.currentIndex % 2 == 0));
+    view.setLocal('odd', (record.currentIndex % 2 == 1));
   }
 
   static bulkRemove(tuples: RecordViewTuple[], viewContainer: ViewContainerRef): RecordViewTuple[] {

modules/angular2/test/core/directives/ng_for_spec.ts

@@ -271,6 +271,44 @@ export function main() {
              });
        }));
 
+    it('should display even items correctly',
+       inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+         var template =
+             '<div><copy-me template="ng-for: var item of items; var isEven=even">{{isEven.toString()}}</copy-me></div>';
+
+         tcb.overrideTemplate(TestComponent, template)
+             .createAsync(TestComponent)
+             .then((rootTC) => {
+               rootTC.debugElement.componentInstance.items = [0, 1, 2];
+               rootTC.detectChanges();
+               expect(rootTC.debugElement.nativeElement).toHaveText('truefalsetrue');
+
+               rootTC.debugElement.componentInstance.items = [2, 1];
+               rootTC.detectChanges();
+               expect(rootTC.debugElement.nativeElement).toHaveText('truefalse');
+               async.done();
+             });
+       }));
+
+    it('should display odd items correctly',
+       inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+         var template =
+             '<div><copy-me template="ng-for: var item of items; var isOdd=odd">{{isOdd.toString()}}</copy-me></div>';
+
+         tcb.overrideTemplate(TestComponent, template)
+             .createAsync(TestComponent)
+             .then((rootTC) => {
+               rootTC.debugElement.componentInstance.items = [0, 1, 2, 3];
+               rootTC.detectChanges();
+               expect(rootTC.debugElement.nativeElement).toHaveText('falsetruefalsetrue');
+
+               rootTC.debugElement.componentInstance.items = [2, 1];
+               rootTC.detectChanges();
+               expect(rootTC.debugElement.nativeElement).toHaveText('falsetrue');
+               async.done();
+             });
+       }));
+
   });
 }