'Empty' namespace not restored in REPL once the define-library form has been used

[alvatar]

This might be intentional, but I believe that for seamless REPL integration of the new define-syntax form, this shouldn't happen:

> (load "define-library")
"/Users/Alvaro/define-library/define-library.o1"
> (define-library (asdf) (import (gambit)))
> (define-library (asdf) (import (gambit)))
*** ERROR IN (console)@3.2 -- Unbound variable: asdf#define-library
1> ,d

Setting namespace to empty solves it, if it is actually a bug.

> (##namespace (""))
> (define-library (asdf) (import (gambit)))

Just adding this form at the end of a define-syntax expansion should be fine, and seems to work in other tests.