Adjusted 2htdp/image's frame primitive so that it does not draw

outside of the bounding box.

collects/2htdp/private/image-more.rkt

@@ -432,12 +432,15 @@
 ;; (useful for debugging images)
 
 (define/chk (frame image)
-  (make-image (make-overlay (image-shape image)
-                            (image-shape 
-                             (rectangle (get-right image)
-                                        (get-bottom image)
-                                        'outline
-                                        'black)))
+  (make-image (make-overlay (image-shape 
+                             (crop 0 0
+                                   (get-right image)
+                                   (get-bottom image)
+                                   (rectangle (get-right image)
+                                              (get-bottom image)
+                                              'outline
+                                              (pen "black" 2 'solid 'round 'round))))
+                            (image-shape image))
               (make-bb (get-right image)
                        (get-bottom image)
                        (get-baseline image))

collects/teachpack/2htdp/scribblings/image-toc.rkt

@@ -135,7 +135,7 @@
       (ellipse 20 10 "solid" "navy"))
     'image
     "54a488e1a5.png")
-   (list '(frame (ellipse 20 20 "outline" "black")) 'image "6a5a617f28.png")
+   (list '(frame (ellipse 40 40 "solid" "gray")) 'image "1a74ac09f8a.png")
    (list
     '(above
       (beside

collects/teachpack/2htdp/scribblings/image.scrbl

@@ -1035,7 +1035,7 @@ the parts that fit onto @racket[scene].
   with a black, single pixel frame drawn around the 
   bounding box of the image.
   
-  @image-examples[(frame (ellipse 20 20 "outline" "black"))]
+  @image-examples[(frame (ellipse 40 40 "solid" "gray"))]
   
   Generally speaking, this function is useful to 
   debug image constructions, i.e., to see where
@@ -1434,6 +1434,12 @@ interior.
                        [r (beside s s s s s s)])
                   (above r r r r r r))]
 
+While this kind of rectangle is not useful for building grids, it 
+is important to be able to build rectangles whose drawing does not
+exceed its bounding box. Specifically, this kind of drawing is used
+by @racket[frame] and @racket[empty-scene] so that the extra drawn pixels
+are not lost if the image is later clipped to its bounding box.
+
 @;-----------------------------------------------------------------------------
 @section{Exporting Images to Disk}