title: Invalidate select when the first option is selected
body: <p>I am going to validate select box (ngOption) by first value (if first value is selected - false, if not - true) and I do not want to use predefined value within select box like this:</p>
  
  <pre><code>&lt;select id="mainVideo" class="form-control"
        ng-model="qtTestData.mainVideo"
        ng-options="mainVideo for mainVideo in mainVideoSources"
        name="mainVideo"
        required&gt;
     &lt;option value=""&gt;-- Please, select a value --&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>So, I have such select box:</p>
  
  <pre><code>&lt;select id="mainVideo" class="form-control" requiredSelect
        ng-model="qtTestData.mainVideo"
        ng-options="mainVideo for mainVideo in mainVideoSources"
        name="mainVideo"
        required&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>My array is:</p>
  
  <pre><code> $scope.mainVideoSources = ['Please, select a value', 'Value1', 'Value2'];
  </code></pre>
  
  <p>I am using this directive to define if first value selected (it means that user did not change the value)</p>
  
  <pre><code>App.directive('requiredSelect', function () {
      return {
          restrict: 'AE',
          require: 'ngModel',
          link: function(scope, element, attributes, ngModel) {
              if (!ngModel) return;
              attributes.requiredSelect = true; 
  
              var validator = function(value) {
                  if ( value != 'Please, select a value' ) { 
                      ngModel.$setValidity('requiredSelect', false);
                      return false;
                  } else {
                      ngModel.$setValidity('requiredSelect', true);
                      return true;
                  }
              };
              ngModel.$formatters.push(validator);
              ngModel.$parsers.unshift(validator);
              attributes.$observe('requiredSelect', function() {
                  validator(ngModel.$viewValue);
              });
          }
      };
  });
  </code></pre>
  
  <p>HTML that should appear if invalid value selected:</p>
  
  <pre><code>&lt;div class="has-error bg-danger" ng-show="qtTestForm.mainVideo.$error.requiredSelect"&gt;
     &lt;p class="text-center"&gt;Oops, something wasn't right&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>But it doesn't work...
  And How can statement <code>(value != 'Please, select a value')</code> be rewritten in Angular way? In JS 
  it's something like this select.selectedIndex == 0  </p>