title: Cannot extract label from form to translate
body: <p>Im using JMS Translation Bundle to extract, and below is my setting:</p>
  
  <p>jms_i18n_routing:</p>
  
  <pre><code>    default_locale: %locale%
      locales: [en]
      strategy: prefix_except_default
  
  jms_translation:
      configs:
          app:
              dirs: [%kernel.root_dir%, %kernel.root_dir%/../src]
              output_dir: %kernel.root_dir%/Resources/translations
              ignored_domains: [routes]
              excluded_names: [*TestCase.php, *Test.php]
              excluded_dirs: [cache, data, logs]
  #            extractors: [jms_translation.file_visitor]
  </code></pre>
  
  <p>however, it seems to not able to pickup and form label from my bundle when run:</p>
  
  <blockquote>
    <p>php app/console translation:extract de --dir=./src/
    --output-dir=./app/Resources/translations</p>
  </blockquote>
  
  <p>And my form looks like this</p>
  
  <pre><code>public function buildForm(FormBuilderInterface $builder, array $options)
      {
          $builder-&gt;add('name', 'text', array(
              'label' =&gt; 'nilead.form.discount.name'
          ))
  
              -&gt;add('value', 'number', array(
                  'label' =&gt; 'nilead.form.discount.number',
                  'constraints' =&gt; array(
                      new GreaterThan(array('value' =&gt; 0))
                  )
              ))
  
              -&gt;add('percentage', 'percent', array(
                  'label' =&gt; 'nilead.form.discount.percentage',
              ))
  
              -&gt;add('code', 'text', array(
                  'label' =&gt; 'nilead.form.discount.code',
              ))
  
              -&gt;add('throughDate', 'date', array(
                  'label' =&gt; 'nilead.form.discount.throughDate',
                  'widget' =&gt; 'single_text',
                  'format' =&gt; 'yyyy-MM-dd',
              ))
  
              -&gt;add('fromDate', 'date', array(
                  'label' =&gt; 'nilead.form.discount.fromDate',
                  'widget' =&gt; 'single_text',
                  'format' =&gt; 'yyyy-MM-dd',
              ))
  
              -&gt;add('usageRemaining', 'text', array(
                  'label' =&gt; 'nilead.form.discount.usageRemaining',
              ))
  
              //-&gt;add('fromDate', 'text')
  
  //            -&gt;add('throughDate', 'text')
  
              -&gt;add('calculator', 'nilead_discount_calculator_choice', array(
                  'empty_value' =&gt; '----',
                  'label' =&gt; 'nilead.form.discount.calculator',
              ))
              -&gt;addEventSubscriber(new BuildDiscountFormListener($this-&gt;calculator, $builder-&gt;getFormFactory()));
  
          $prototypes = array();
          $prototypes['calculators'] = array();
  
          foreach ($this-&gt;calculator-&gt;getCalculators() as $calculator) {
              $calculatorObj = $this-&gt;calculator-&gt;get($calculator);
              $prototype = $builder-&gt;create('settings', $calculatorObj-&gt;getConfigurationFormType())-&gt;getForm();
  
              $prototypes['calculators'][$calculator] = $prototype;
          }
          $builder-&gt;setAttribute('prototypes', $prototypes);
      }
  </code></pre>