Symbolic links in recipes

I just tried to create a vagrant recipe, but there was an issue at the post stage

```pytb
An unexpected error has occurred, please consider sending the
following traceback to the conda GitHub issue tracker at:

    https://github.com/ContinuumIO/conda/issues

Include the output of the command 'conda info' in your report.


Traceback (most recent call last):
  File "/Users/aaronmeurer/anaconda3/bin/conda", line 5, in <module>
    sys.exit(main())
  File "/Users/aaronmeurer/Documents/Continuum/conda/conda/cli/main.py", line 186, in main
    args.func(args, p)
  File "/Users/aaronmeurer/Documents/Continuum/conda/conda/cli/main_build.py", line 169, in execute
    build.build(m, pypi=args.pypi)
  File "/Users/aaronmeurer/Documents/Continuum/conda/conda/builder/build.py", line 180, in build
    post_build(sorted(files2 - files1))
  File "/Users/aaronmeurer/Documents/Continuum/conda/conda/builder/post.py", line 184, in post_build
    fix_permissions(files)
  File "/Users/aaronmeurer/Documents/Continuum/conda/conda/builder/post.py", line 178, in fix_permissions
    st = os.stat(path)
FileNotFoundError: [Errno 2] No such file or directory: '/Users/aaronmeurer/anaconda3/envs/_build/vagrant/embedded/include/ruby-1.9.1/x86_64-darwin12.2.1'
```

See https://github.com/ContinuumIO/conda-recipes/tree/master/vagrant