HHVM's repo loader is super finicky about permissions, and gives terrible error messages

If HHVM isn't able to read and write to both the repo and its enclosing directory, it gives the very misleading error message

```
Failed to load Repo::GlobalData: /home/vagrant/.hhvm.hhbc: No rows in main.GlobalData_6ba408ef27e1fc7820c8bd6352989f40c1acb812. Did you forget to compile that file with this HHVM version?
```

Ideally HHVM would care less about permissions (why does it need to write in repo auth mode? why does it care about the enclosing directory?) but at the very least, can give a more useful error message.