title: virtualenv with --always-copy throws error "Operation not permitted"
body: <p>I'm trying to run virtualenv without symlinking python2.7 but I get permission errors when I use the flag --always-copy.</p>
  
  <pre><code>virtualenv --always-copy myenv
  
  Traceback (most recent call last):  
  
    File "/usr/local/bin/virtualenv", line 11, in &lt;module&gt;  
      sys.exit(main())  
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 711, in main  
      symlink=options.symlink)  
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 924, in create_environment  
      site_packages=site_packages, clear=clear, symlink=symlink))  
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 1129, in install_python  
      copyfile(join(stdlib_dir, fn), join(lib_dir, fn), symlink)  
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 355, in copy file  
      copyfileordir(src, dest, symlink)  
    File "/Library/Python/2.7/site-packages/virtualenv.py", line 327, in copyfileordir  
      shutil.copytree(src, dest, symlink)  
    File   "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 208, in copytree  
      raise Error, errors  
  shutil.Error:  
  [('/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/config/config.c', '/Users/user1/myenv/lib/python2.7/config/config.c', "[Errno 1] Operation not permitted: '/Users/user1/myenv/lib/python2.7/config/config.c'"), ...
  </code></pre>