Add glob method to PathHelper which escapes \ characters

This should solve the tummy ache caused by Windows paths which use the `"\\"` separator.

See: https://github.com/opscode/chef/issues/2078

\cc @opscode/client-engineers 
jenkins may have rotted my brain, but its not obvious why this wouldn't work...

```
.gsub(/\\/, '\')
```

if i'm missing something it could definitely use a comment...