title: Can't install matplotlib on OS X with PIP
body: <p>This is my first time setting up matplotlib.<br>
  I'm on OS X Lion 10.7 (build 11A511s, so no updates done to the initial release of OS X Lion).<br>
  I am using virtualenv and pip to do the installation.<br>
  I'm aware of the incompatibility with libpng 1.5, so I didn't just run "pip install matplotlib"... instead...<br>
  I tried running this from inside the virtualenv:</p>
  
  <p><code>pip install -e git+https://github.com/matplotlib/matplotlib#egg=matplotlib-dev</code></p>
  
  <p>Looks like it starts installing, but then I get this error:</p>
  
  <pre><code>/Users/myusername/.virtualenvs/nltk/lib/python2.7/site-packages/numpy/core/include/numpy/
  __multiarray_api.h:1532: warning: ‘int _import_array()’ defined but not used
  
  lipo: can't open input file: /var/folders/wy/s1jr354d4xx7dk0lpdpbpsbc0000gn/T/
  /ccfNUhyq.out (No such file or directory)
  
  error: command 'llvm-gcc-4.2' failed with exit status 1
  
  ----------------------------------------
  Command /Users/sameerfx/.virtualenvs/nltk/bin/python -c "import setuptools; __file__=
  '/Users/sameerfx/.virtualenvs/nltk/src/matplotlib/setup.py'; exec(compile(open(__file__
  ).read().replace('\r\n', '\n'), __file__, 'exec'))" develop --no-deps failed with error code 1
  Storing complete log in /Users/sameerfx/.pip/pip.log
  </code></pre>