feat(http): add support for JSONP requests

Closes #2905
Closes #2818

modules/examples/src/jsonp/jsonp_comp.ts

@@ -0,0 +1,23 @@
+import {Component, View, NgFor} from 'angular2/angular2';
+import {Jsonp} from 'angular2/http';
+import {ObservableWrapper} from 'angular2/src/facade/async';
+
+@Component({selector: 'jsonp-app'})
+@View({
+  directives: [NgFor],
+  template: `
+    <h1>people</h1>
+    <ul class="people">
+      <li *ng-for="#person of people">
+        hello, {{person['name']}}
+      </li>
+    </ul>
+  `
+})
+export class JsonpCmp {
+  people: Object;
+  constructor(jsonp: Jsonp) {
+    ObservableWrapper.subscribe(jsonp.get('./people.json?callback=JSONP_CALLBACK'),
+                                res => this.people = res.json());
+  }
+}