title: Pybabel generates empty pot file with jinja2
body: <p>I'm using Flask, Flask-Babel and Jinja2. I'm trying to generate the .pot file. That what I did so far.</p>
  <p><strong>My babel.cfg looks like this:</strong></p>
  <pre><code>[python: **.py]
  
  [jinja2: **.html]
  encoding = utf-8
  extensions=jinja2.ext.autoescape,jinja2.ext.with_
  </code></pre>
  <p><strong>I'm initialize Flask-Babel with my app like this:</strong></p>
  <pre><code># Babel init
  babel = Babel(app)
  app.config['BABEL_DEFAULT_LOCALE'] = 'en'
  </code></pre>
  <p><strong>In my templates directory I do have homepage.html:</strong></p>
  <pre><code>...
  &lt;div class=&quot;news-wrapper&quot;&gt;
      &lt;p class=&quot;quote&quot;&gt;{{ gettext('Hey there') }}&lt;/p&gt;
      &lt;p class=&quot;quote&quot;&gt;{% trans %}Trying 42{% endtrans %}&lt;/p&gt;
      &lt;p class=&quot;quote&quot;&gt;{{ _('Maybe like this?') }}&lt;/p&gt;
  &lt;/div&gt;
  ...
  </code></pre>
  <p><strong>Then running this command(while I'm in my virtualenv):</strong></p>
  <pre><code>pybabel extract -F babel.cfg -o messages.pot .
  </code></pre>
  <p><strong>One of the outputs lines is:</strong></p>
  <pre><code>extracting messages from templates/homepage.html (extensions=&quot;jinja2.ext.autoescape,jinja2.ext.with_&quot;, encoding=&quot;utf-8&quot;)
  </code></pre>
  <p><strong>And it is generates a messages.pot file with this content:</strong></p>
  <pre><code># Translations template for PROJECT.
  # Copyright (C) 2015 ORGANIZATION
  # This file is distributed under the same license as the PROJECT project.
  # FIRST AUTHOR &lt;EMAIL@ADDRESS&gt;, 2015.
  #
  #, fuzzy
  msgid &quot;&quot;
  msgstr &quot;&quot;
  &quot;Project-Id-Version: PROJECT VERSION\n&quot;
  &quot;Report-Msgid-Bugs-To: EMAIL@ADDRESS\n&quot;
  &quot;POT-Creation-Date: 2015-04-21 10:06+0300\n&quot;
  &quot;PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n&quot;
  &quot;Last-Translator: FULL NAME &lt;EMAIL@ADDRESS&gt;\n&quot;
  &quot;Language-Team: LANGUAGE &lt;LL@li.org&gt;\n&quot;
  &quot;MIME-Version: 1.0\n&quot;
  &quot;Content-Type: text/plain; charset=utf-8\n&quot;
  &quot;Content-Transfer-Encoding: 8bit\n&quot;
  &quot;Generated-By: Babel 1.3\n&quot;
  </code></pre>
  <p>The file does not have my translations.</p>
  <p>I get no errors or warnings, pybabel just can't find the <code>gettext</code> variations in jinja2 files. <strong>BUT</strong> when I use the <code>gettext</code> in  a .py file <strong>it is</strong> working just fine.</p>
  <p>Do I miss something?</p>