scheme/gui/base: fix module-attach problem in `make-gui-base-namespace'

The `scheme/base' module had become unreachable from the `mred' module.
While that normally would be a good thing, it lead to troublesome
multiple instantiations of `scheme/base' that caused problems for
attaching further modules to the namespace.

collects/mred/private/mred.rkt

@@ -3,6 +3,7 @@
                  define-namespace-anchor
                  namespace-anchor->empty-namespace
                  make-base-empty-namespace)
+           (only scheme/base) (only scheme/class) ; so that `make-gui-namespace' attaches them
            racket/class
            racket/draw racket/snip
            file/resource

collects/tests/gracket/racket-ns.rkt

@@ -0,0 +1,9 @@
+#lang racket/base
+(require racket/gui/base
+         racket/gui/dynamic)
+;; Don't change this program to use `racket'; ths point
+;; is to test `racket/gui/base' exports
+
+(let ([ns ((gui-dynamic-require 'make-gui-namespace))]
+      [orig-ns (current-namespace)])
+  (namespace-attach-module orig-ns 'racket/base ns))

collects/tests/gracket/scheme-ns.rkt

@@ -0,0 +1,9 @@
+#lang scheme/base
+(require scheme/gui/base
+         scheme/gui/dynamic)
+;; Don't change this program to use `racket'; ths point
+;; is to test `scheme/gui/base' exports
+
+(let ([ns ((gui-dynamic-require 'make-gui-namespace))]
+      [orig-ns (current-namespace)])
+  (namespace-attach-module orig-ns 'scheme/base ns))