fix(angular.bootstrap): only allow angular to load once

This is hard to test as a unit-test, since it involves the actual loading
of angular, but it turns out that it is easy to test using a protractor
e2e test.

Closes #5863
Closes #5587

src/Angular.js

@@ -1241,6 +1241,41 @@ function angularInit(element, bootstrap) {
  * Note that ngScenario-based end-to-end tests cannot use this function to bootstrap manually.
  * They must use {@link ng.directive:ngApp ngApp}.
  *
+ * Angular will detect if it has been loaded into the browser more than once and only allow the
+ * first loaded script to be bootstrapped and will report a warning to the browser console for
+ * each of the subsequent scripts.   This prevents strange results in applications, where otherwise
+ * multiple instances of Angular try to work on the DOM.
+ *
+ * <example name="multi-bootstrap" module="multi-bootstrap">
+ * <file name="index.html">
+ * <script src="../../../angular.js"></script>
+ * <div ng-controller="BrokenTable">
+ *   <table>
+ *   <tr>
+ *     <th ng-repeat="heading in headings">{{heading}}</th>
+ *   </tr>
+ *   <tr ng-repeat="filling in fillings">
+ *     <td ng-repeat="fill in filling">{{fill}}</td>
+ *   </tr>
+ * </table>
+ * </div>
+ * </file>
+ * <file name="controller.js">
+ * var app = angular.module('multi-bootstrap', [])
+ *
+ * .controller('BrokenTable', function($scope) {
+ *     $scope.headings = ['One', 'Two', 'Three'];
+ *     $scope.fillings = [[1, 2, 3], ['A', 'B', 'C'], [7, 8, 9]];
+ * });
+ * </file>
+ * <file name="protractor.js" type="protractor">
+ * it('should only insert one table cell for each item in $scope.fillings', function() {
+ *  expect(element.all(by.css('td')).count())
+ *      .toBe(9);
+ * });
+ * </file>
+ * </example>
+ *
  * @param {Element} element DOM element which is the root of angular application.
  * @param {Array<String|Function|Array>=} modules an array of modules to load into the application.
  *     Each item in the array should be the name of a predefined module or a (DI annotated)

src/angular.suffix

@@ -1,3 +1,9 @@
+  if (window.angular.bootstrap) {
+    //AngularJS is already loaded, so we can return here...
+    console.log('WARNING: Tried to load angular more than once.');
+    return;
+  }
+
   //try to bind to jquery now so that one can write angular.element().read()
   //but we will rebind on bootstrap again.
   bindJQuery();