Fix compiled-bitmap and compiled-bitmap-list on 2x bitmaps, lossy compression

This fixes the docs for `compiled-bitmap-list`. Icons in DrRacket were immune,
because they're stored in modules as PNG bytes.

Please merge to v6.1
(cherry picked from commit 1f7b452920)

pkgs/images-pkgs/images-lib/images/compile-time.rkt

@@ -34,7 +34,7 @@
     (define alpha-p (open-output-bytes))
     (send alpha-bm save-file alpha-p 'jpeg quality)
     
-    (send bm get-argb-pixels 0 0 w h bs #f)
+    (send bm get-argb-pixels 0 0 w h bs #f #:unscaled? #t)
     (define rgb-bm (make-bitmap w h #f))
     (send rgb-bm set-argb-pixels 0 0 w h bs #f)
     (define rgb-p (open-output-bytes))