title: import matplotlib.pyplot as plt fails with error about python-tk
body: <p>I tried to import matplotlib.pyplot, however received an error relating to python-tk not being installed. It appears to be installed but I still appear to be receiving the error. Any help would be appricated. For further info, the output is below. Many thanks.</p>
  
  <pre><code>    $ ipython
      Python 2.7.7 (default, Jun  3 2014, 16:16:56)
      Type "copyright", "credits" or "license" for more information.
  
      IPython 2.1.0 -- An enhanced Interactive Python.
      ?         -&gt; Introduction and overview of IPython's features.
      %quickref -&gt; Quick reference.
      help      -&gt; Python's own help system.
      object?   -&gt; Details about 'object', use 'object??' for extra details.
  
      In [1]: import numpy as np
  
      In [2]: import matplotlib.pyplot as plt
      ---------------------------------------------------------------------------
      ImportError                               Traceback (most recent call last)
      &lt;ipython-input-2-eff513f636fd&gt; in &lt;module&gt;()
      ----&gt; 1 import matplotlib.pyplot as plt
  
      /usr/lib/pymodules/python2.7/matplotlib/pyplot.py in &lt;module&gt;()
           96
           97 from matplotlib.backends import pylab_setup
      ---&gt; 98 _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
           99
          100
  
      /usr/lib/pymodules/python2.7/matplotlib/backends/__init__.pyc in pylab_setup()
           26     # imports. 0 means only perform absolute imports.
           27     backend_mod = __import__(backend_name,
      ---&gt; 28                              globals(),locals(),[backend_name],0)
           29
           30     # Things we pull in from all backends
  
      /usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py in &lt;module&gt;()
            6 import os.path
            7
      ----&gt; 8 import Tkinter as Tk, FileDialog
            9
           10 # Paint image to Tk photo blitter extension
  
      /usr/lib/python2.7/lib-tk/Tkinter.py in &lt;module&gt;()
           40     import _tkinter
           41 except ImportError, msg:
      ---&gt; 42     raise ImportError, str(msg) + ', please install the python-tk package'
           43 tkinter = _tkinter # b/w compat for export
           44 TclError = _tkinter.TclError
  
      ImportError: libBLT.2.4.so.8.5: cannot open shared object file: No such file or directory, please install the python-tk package
  </code></pre>