title: ng-disabled is failing when put more than one expression
body: <p>In one scenario I want to use a radio for selection of options and after selection explicitly i want the user to do the confirmation for which i have used confirm method of javascript. after confirmation for the selection only the next button should get enabled. 
  have a look at below code</p>
  
  <p>HTML</p>
  
  <pre><code>  &lt;body ng-controller="MainCtrl"&gt;
    &lt;div ng-repeat="person in names"&gt;
  
      &lt;input class="d-radio__input" ng-model="$parent.selectedCustomer" type="radio" ng-value="person" value="{{person.name}}" name="radio" ng-click="confirm()" required /&gt; {{person.name}}
  
    &lt;/div&gt;
    &lt;button&gt;Back&lt;/button&gt;
    &lt;button ng-click="next()" ng-disabled="selectedCustomer =='' &amp;&amp; confirmation == 0 "&gt;Next&lt;/button&gt;
  &lt;/body&gt;
  </code></pre>
  
  <p>Javascript</p>
  
  <pre><code>    app.controller('MainCtrl', function($scope) {
    $scope.selectedCustomer ='';
    $scope.confirmation=0;
    $scope.names = [{name:"Mayur"},{name:"Sameer"}];
  
                  $scope.next = function () {
                      $scope.navigator =  $scope.navigator + 1 ;
                      console.log($scope.navigator)
                  };
                  $scope.confirm = function (location) {
                      var r = confirm("Click Ok to continue the offboarding process for (" + $scope.selectedCustomer.customerName + ")");
                      if (r === true) {
                          $scope.confirmation = 1;
                          console.log($scope.confirmation );
                      } else {
                          $scope.confirmation = 0;
                          console.log($scope.confirmation );
                      }
                  }
  });
  </code></pre>
  
  <p>So when i select a name immediately it is enabling the next button irrespective of what i press in the confirmation dialogue box. But when i keep only one conditional expression to evaluate for ng-disabled then it is working fine. 
   Not sure how i can add more than one condition in ng-disabled.</p>
  
  <p>Please let me know if I am doing something wrong. </p>
  
  <p>have a look at <a href="http://plnkr.co/edit/Wl5u6471W5wpxDqGX5tn" rel="nofollow">Plunker</a></p>