fix 2htdp/image for text-only mode and add a test case that

covers improvements from 8fb8f56

pkgs/gui-pkgs/gui-lib/mrlib/image-core-wxme.rkt

@@ -10,5 +10,8 @@
    (class* object% (snip-reader<%>)
      (define/public (read-header vers stream) (void))
      (define/public (read-snip text? cvers stream)
-       (snipclass-bytes->image (send stream read-raw-bytes '2htdp/image)))
+       (define bytes (send stream read-raw-bytes '2htdp/image))
+       (if text?
+           #"."
+           (snipclass-bytes->image bytes)))
      (super-new))))

pkgs/htdp-pkgs/htdp-test/2htdp/tests/test-image.rkt

@@ -2567,7 +2567,8 @@
   (test (equal? (image-baseline (list-ref washed 2))
                 (image-height (list-ref washed 2)))
         =>
-        #f))
+        #f)
+  (test washed => (list img1 img2 img3)))
 
 (test (convertible? (circle 20 "solid" "red")) => #t)
 (test (bytes? (convert (circle 20 "solid" "red") 'png-bytes)) => #t)