Pathname objects may be in the LOAD_PATH, causing a crash on #chomp

I had this exception occurring when manually reporting an exception.

```
undefined method `chomp' for #<Pathname:/home/apps/user/releases/20140520085231/lib>
```

It appears that while every other effort is made to ensure a string is made available, the final call may be calling `chomp` on something such as a `Pathname`. This PR ensures the prefix is brought down to a String before calling `chomp`.