title: cannot import local module inside virtual environment from subfolder
body: <p>I am working inside a virtual environment created via <code>pyenv virtualenv</code> and my folder structure looks as follows </p>
  
  <pre><code>ProjectFolder (virtual env)
      Subfolder
          modulea.py
          __init__.py
      main.py
  </code></pre>
  
  <p>in the <code>main.py</code> I want to call a function defined in modulea.py. However, </p>
  
  <pre><code>from Subfolder.modulea import function 
  </code></pre>
  
  <p>yields the error </p>
  
  <blockquote>
    <p>no module named Subfolder.modulea ; Subfolder is not a package.</p>
  </blockquote>
  
  <p>when I reproduce an analog structure with some testfiles outside the virtual environments, all works well. Also, when I move <code>modulea.py</code> into the ProjectFolder the import works well.</p>