fix(buttons): respect disabled attribute

- Ensure disabled attribute is respected due to a change in Bootstrap 3.3.5 CSS

Author: wesleycho

Diff for: src/buttons/buttons.js

@@ -64,6 +64,10 @@ angular.module('ui.bootstrap.buttons', [])
 
       //ui->model
       element.bind(buttonsCtrl.toggleEvent, function () {
+        if ('disabled' in attrs) {
+          return;
+        }
+
         scope.$apply(function () {
           ngModelCtrl.$setViewValue(element.hasClass(buttonsCtrl.activeClass) ? getFalseValue() : getTrueValue());
           ngModelCtrl.$render();

Diff for: src/buttons/test/buttons.spec.js

@@ -81,6 +81,23 @@ describe('buttons', function () {
       expect($scope.model).toEqual(2);
     });
 
+    it('should not toggle when disabled - issue 4013', function () {
+      $scope.model = 1;
+      $scope.falseVal = 0;
+      var btn = compileButton('<button disabled ng-model="model" btn-checkbox btn-checkbox-true="falseVal">click</button>', $scope);
+
+      expect(btn).not.toHaveClass('active');
+      expect($scope.model).toEqual(1);
+
+      btn.click();
+
+      expect(btn).not.toHaveClass('active');
+
+      $scope.$digest();
+      
+      expect(btn).not.toHaveClass('active');
+    });
+
     describe('setting buttonConfig', function () {
       var originalActiveClass, originalToggleEvent;