title: Troubleshooting 'Variable "value" does not exist' when customising text_widget
body: <p>Trying to customize Symfony2 form to produce html code looking like the following example:</p>
  
  <pre><code>&lt;div class="cform_box"&gt;
    &lt;div&gt;&lt;label&gt;First name:&lt;/label&gt;&lt;/div&gt;
    &lt;input name="" type="text" id="" class="TextBox" /&gt;
  &lt;/div&gt;
  &lt;div class="cform_box" style="height:auto"&gt;
     &lt;div&gt;&lt;label&gt;Message:&lt;/label&gt;&lt;/div&gt;
    &lt;textarea name="" rows="10" cols="38" id="" class="TextBox" style="height:100px;" /&gt;&lt;/textarea&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>My form code :</p>
  
  <pre><code>$builder-&gt;add('name', 'text', array('label' =&gt;'First Name:'));
  $builder-&gt;add('message', 'textarea', array('label' =&gt;'Message:'));
  </code></pre>
  
  <p>The template <code>contact.html.twig</code>:</p>
  
  <pre><code>{% form_theme form _self %}
  {% block text_widget %}
  {% spaceless %}
      &lt;input type="text" class='TextBox' {% if value is not empty %}value="{{ value }}"     {% endif %}/&gt;
  {% endspaceless %}
  {% endblock %}
  {% block textarea_widget %}
  {% spaceless %}
      &lt;div class="textarea_widget"&gt;
          &lt;textarea rows="10" cols="38" id="{{ id }}" class="TextBox" style="height:100px;"&gt;{{ value }}&lt;/textarea&gt;
      &lt;/div&gt;
  {% endspaceless %}
  {% endblock textarea_widget %}
  
  &lt;div class="cform_box"&gt;    
      &lt;div&gt;{{ form_label(form.name) }}&lt;/div&gt;{{ form_widget(form.name) }}
  &lt;/div&gt;
  &lt;div class="cform_box" style="height:auto"&gt;
      &lt;div&gt;{{ form_label(form.message) }}&lt;/div&gt;{{ form_widget(form.message) }}
  &lt;/div&gt;
  </code></pre>
  
  <p>I am getting either <code>Variable "value" does not exist in contact.html.twig</code> or <code>Variable "id" does not exist in form_div_layout.html.twig</code> if I comment <code>{% block text_widget %}</code> out.</p>
  
  <p>I'm using Symfony 2.0.15</p>