Ensures that loading pry inside config doesn't explode

See #1051

I was looking through the tracker for something to work on. This seemed like low hanging fruit.

This deals with the stack explosion, and means you can get out of pry without having to `raise SystemExit`.

It'd be nice at some point to actually be able to debug your pryrc with pry, but it'll take me a bit to work out the required magic.