title: Error using tkagg backend
body: <p>I am using the following setup:</p>
  
  <pre><code>Python 3.5.2 + Matplotlib 1.5.x (Raspberry Pi)
  </code></pre>
  
  <p>I have added <code>backend :tkagg</code> to my rc file.</p>
  
  <p>If I run <code>get_backend()</code> it returns <code>"tkagg"</code></p>
  
  <p>However, when I try to import <code>matplotlib</code> as follows:</p>
  
  <pre><code> Python 3.4.2 (default, Oct 19 2014, 13:31:11) 
   [GCC 4.9.1] on linux
   Type "copyright", "credits" or "license()" for more information.
  
   &gt;&gt;&gt; import matplotlib as mpl
   &gt;&gt;&gt; mpl.use('tkagg')
   &gt;&gt;&gt; import matplotlib.pyplot as plt
  </code></pre>
  
  <p>I receive the following traceback:</p>
  
  <pre><code> Traceback (most recent call last):
   File "&lt;pyshell#2&gt;", line 1, in &lt;module&gt;
   import matplotlib.pyplot as plt
  
  File "/usr/local/lib/python3.4/dist-packages/matplotlib-1.5.0-py3.4-linux-armv7l.egg/matplotlib/pyplot.py", line 114, in &lt;module&gt;
  backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/usr/local/lib/python3.4/dist-packages/matplotlib-1.5.0-py3.4-linux-armv7l.egg/matplotlib/backends/__init__.py", line 32, in pylab_setup
  globals(),locals(),[backend_name],0)
  File "/usr/local/lib/python3.4/dist-packages/matplotlib-1.5.0-py3.4-linux-armv7l.egg/matplotlib/backends/backend_tkagg.py", line 13, in &lt;module&gt;
  import matplotlib.backends.tkagg as tkagg
  File "/usr/local/lib/python3.4/dist-packages/matplotlib-1.5.0-py3.4-linux-armv7l.egg/matplotlib/backends/tkagg.py", line 9, in &lt;module&gt;
  from matplotlib.backends import _tkagg
   ImportError: cannot import name '_tkagg'
  </code></pre>
  
  <p>Why isn't <code>matplotlib</code> being imported correctly?</p>