[r7rs] 'environment' wrongly imports all symbols from r7rs module

[rgherdt]

The procedure environment from (scheme eval) imports all symbols from r7rs by default, leading to a wrong behavior:

(import (scheme eval))
(eval '(+ 1 3) (environment '(except (scheme base) +)))
.
.
.
4

The expected behavior is an "unbound variable: +" error.

I'll upload a patch (thanks Felix).

[rgherdt]

Patch to bug involving 'environment' in scheme.eval.scm