title: Tkinter.StringVar() throws an exception
body: <p>I have python <code>2.7.2-4</code> (Archlinux), and from</p>
  
  <pre><code>import Tkinter
  Tkinter.StringVar()
  </code></pre>
  
  <p>results</p>
  
  <pre><code>Traceback (most recent call last):
    File "/tmp/foo.py", line 3, in &lt;module&gt;
      foo = Tkinter.StringVar()
    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 251, in __init__
      Variable.__init__(self, master, value, name)
    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 182, in __init__
      self._tk = master.tk
  AttributeError: 'NoneType' object has no attribute 'tk'
  Exception AttributeError: "StringVar instance has no attribute '_tk'" in &lt;bound method StringVar.__del__ of &lt;Tkinter.StringVar instance at 0x1815710&gt;&gt; ignored
  </code></pre>