title: Karma: Check not flushed requests
body: <p>I write tests for angular app using karma, is any way i can check not flushed requests before $httpBacked.flush()? i need this because i dont know is request sent or not and if no, $httpBacked.flush() cause exception.</p>
  
  <p>i need something like this: </p>
  
  <pre><code>it('should', function() {
      if($httpBackend.isRequestsPresent()) { 
          $httpBackend.flush(); 
      }
  })
  </code></pre>