title: py.test: Temporary folder for the session scope
body: <p>The <code>tmpdir</code> fixture in py.test uses the <code>function</code> scope and thus isn't available in a fixture with a broader scope such as <code>session</code>. However, this would be useful for some cases such as setting up a temporary PostgreSQL server (which of course shouldn't be recreated for each test).</p>
  
  <p>Is there any clean way to get a temporary folder for a broader scope that does not involve writing my own fixture and accessing internal APIs of py.test?</p>