title: Python gives NotImplementedError for posix grp functions on AIX
body: <p>I found this problem while using python to extract a tar file, using <code>tarfile.extractall</code>. The function works on other OS, but on AIX I get an error originating from <code>getgrnam</code>.</p>
  
  <p>Here is a very simple test invoking <code>getgrnam</code> only:  </p>
  
  <pre><code>Jython 2.5.2 (Release_2_5_2:7206, Mar 2 2011, 23:12:06)
  [IBM J9 VM (IBM Corporation)] on java1.5.0
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt;
  &gt;&gt;&gt; import grp
  &gt;&gt;&gt;
  &gt;&gt;&gt; file = "test.txt"
  &gt;&gt;&gt;
  &gt;&gt;&gt; grp.getgrnam(file)
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/tmp/jython.jar/Lib/grp.py", line 67, in getgrnam
  NotImplementedError: getgrnam unimplemented
  </code></pre>
  
  <p>Any idea why this is happening and what a solution might be?</p>