fix(modal): properly animate backdrops on each modal opening

Closes #1267

src/modal/modal.js

@@ -62,7 +62,9 @@ angular.module('ui.bootstrap.modal', [])
       restrict: 'EA',
       replace: true,
       templateUrl: 'template/modal/backdrop.html',
-      link: function (scope, element, attrs) {
+      link: function (scope) {
+
+        scope.animate = false;
 
         //trigger CSS transitions
         $timeout(function () {

src/modal/test/modal.spec.js

@@ -375,6 +375,22 @@ describe('$modal', function () {
         expect($document).toHaveModalOpenWithContent('Static backdrop', 'div');
         expect($document).toHaveBackdrop();
       });
+
+      it('should animate backdrop on each modal opening', function () {
+
+        var modal = open({ template: '<div>With backdrop</div>' });
+        var backdropEl = $document.find('body > div.modal-backdrop');
+        expect(backdropEl).not.toHaveClass('in');
+
+        $timeout.flush();
+        expect(backdropEl).toHaveClass('in');
+
+        dismiss(modal);
+        modal = open({ template: '<div>With backdrop</div>' });
+        backdropEl = $document.find('body > div.modal-backdrop');
+        expect(backdropEl).not.toHaveClass('in');
+
+      });
     });
 
     describe('custom window classes', function () {