title: DistutilsOptionError: must supply either home or prefix/exec-prefix -- not both
body: <p>I've been usually installed python packages through pip.</p>
  
  <p>For Google App Engine, I need to install packages to another target directory.</p>
  
  <p>I've tried:</p>
  
  <blockquote>
    <p>pip install -I flask-restful --target ./lib</p>
  </blockquote>
  
  <p>but it fails with:</p>
  
  <blockquote>
    <p>must supply either home or prefix/exec-prefix -- not both</p>
  </blockquote>
  
  <p>How can I get this to work?</p>