Cannot use define-language in the REPL.

[LeifAndersen]

Inside of the repl, if I run the following code, I get an error:

> (require nanopass/base)
> (define-language Lsrc
    (terminals
      (number (n)))
    (Expr (e)
      n
      (+ e1 e2)))
; readline-input:2.17: define-unparser: unrecognized language name
;   at: Lsrc
; [,bt for context]

I'm not sure what the problem is here yet, but I suspect we are expecting to be in a module context somewhere, which doesn't seem to work.

[LeifAndersen]

Commit #162 fixes this.