title: Virtualenv failing when creating an enviroment
body: <p>I don't know the reason, but the function mkvirtualenv is ending in the following error:</p>
  
  <pre><code>LEP:~ lep$ mkvirtualenv myenvironment
  New python executable in myenvironment/bin/python
  Installing setuptools, pip, wheel...
  Complete output from command /Users/lep/.virtuale...vironment           /bin/python -c "import sys, pip; sys...d\"] + sys.argv[1:]))" setuptools pip wheel:
    Traceback (most recent call last):
    File "&lt;string&gt;", line 1, in &lt;module&gt;
    File "/Users/lep/anaconda/lib/python2.7/site-packages/virtualenv_support/pip-7.1.0-py2.py3-none-any.whl/pip/__init__.py", line 13, in &lt;module&gt;
    File "/Users/lep/anaconda/lib/python2.7/site-packages/virtualenv_support/pip-7.1.0-py2.py3-none-any.whl/pip/utils/__init__.py", line 15, in &lt;module&gt;
   File "/Users/lep/anaconda/lib/python2.7/zipfile.py", line 6, in &lt;module&gt;
  import io
   File "/Users/lep/anaconda/lib/python2.7/io.py", line 51, in &lt;module&gt;
  import _io
  ImportError: dlopen(/Users/lep/.virtualenvs/myenvironment/lib/python2.7/lib-dynload/_io.so, 2): Symbol not found: __PyErr_ReplaceException
    Referenced from: /Users/lep/.virtualenvs/myenvironment/lib/python2.7/lib-dynload/_io.so
    Expected in: dynamic lookup
  
  ----------------------------------------
  ...Installing setuptools, pip, wheel...done.
    Traceback (most recent call last):
    File "/Users/lep/anaconda/bin/virtualenv", line 11, in &lt;module&gt;
  sys.exit(main())
    File "/Users/lep/anaconda/lib/python2.7/site-packages/virtualenv.py", line 832, in main
  symlink=options.symlink)
    File "/Users/lep/anaconda/lib/python2.7/site-packages/virtualenv.py", line 1004, in create_environment
  install_wheel(to_install, py_executable, search_dirs)
       File "/Users/lep/anaconda/lib/python2.7/site-packages/virtualenv.py", line 969, in install_wheel
  'PIP_NO_INDEX': '1'
    File "/Users/lep/anaconda/lib/python2.7/site-packages/virtualenv.py", line 910, in call_subprocess
      % (cmd_desc, proc.returncode))
   OSError: Command /Users/lep/.virtuale...vironment/bin/python -c "import sys, pip; sys...d\"] + sys.argv[1:]))" setuptools pip wheel failed with error code 1
  </code></pre>
  
  <p>It is was working before and now I am getting this error. Does someone can help me?</p>
  
  <p>Thanks in advance,</p>
  
  <p>Rhenan</p>