fix(a): Opera click event (Bootstrap DropDownToggle and so on)

Prevents Opera from incorrectly navigating on link click and fixes Bootstrap DropDown behavior.

Closes https://github.com/angular/angular.js/issues/1225 , https://github.com/angular/angular.js/issues/1651 , https://github.com/angular/angular.js/issues/1674 , https://github.com/angular/angular.js/issues/1662 , https://github.com/angular/angular.js/issues/1729