Audit formulœ for easy-install.pth files

These are unhelpful and will probably cause link conflicts; they result from failing to provide --single-version-externally-managed to setuptools.
Can this be simplified to:

```rb
pth_found = Dir["#{lib}/python{2.7,3.4}/site-packages/easy_install.pth"].map { |f| File.dirname(f) }
```

?