title: Angular expressions in $watch trigger twice
body: <p>Why does this <code>$watch</code> fire twice when a simple comparison is passed as the watchExpression?</p>
  
  <pre class="lang-js prettyprint-override"><code>$scope.foo = 0;  // simple counter
  
  $scope.$watch('foo &gt; 4', function() {
    console.log("foo is greater than 4: ", $scope.foo);
  });
  </code></pre>
  
  <p>The listener fires when the page loads, when <code>foo</code> is <code>0</code>, then once more (and only once more) when the value of <code>foo</code> goes above 4.</p>
  
  <p>Why does the listener fire when the page loads? And why doesn't it continue to fire when <code>foo</code> is greater than 4?</p>
  
  <p>I set up a simple plunkr to show what's happening: <a href="http://plnkr.co/edit/ghYRl9?p=preview">http://plnkr.co/edit/ghYRl9?p=preview</a></p>