title: Toggle class between two buttons in Angular but restrict to prevent same button from changing class
body: <p>Trying to create some very basic functionality which basically makes two buttons behave like radio buttons. Have two buttons that are used to show/hide different content based on what is shown. So it is working as expected except for it is changing on any click. So if I click the same button twice then it changes the class. I only need it to change if the other button is clicked: </p>
  
  <pre><code>&lt;button class="someClass" ng-class="{true: 'green', false: 'blue'}        [!yupNope.isSelected]" ng-click="yupNope.isSelected = !yupNope.isSelected"&gt;YES&lt;/button&gt;
     &lt;button class="someClass" ng-class="{false: 'green', true: 'yupNope'}[!yupNope.isSelected]" ng-click="yupNope.isSelected = !yupNope.isSelected"&gt;NO&lt;/button&gt;
  </code></pre>
  
  <p>So if Yes is clicked then it should update and No should too. But if Yes is clicked again before No is clicked then there should be no change. </p>
  
  <p>Here is a Plunkr to play with: </p>
  
  <p><a href="http://plnkr.co/edit/3hDVCYaQVyTaxrE4IZOl?p=preview" rel="nofollow">Plunkr Demo</a></p>