Improve type specifications for bitmap handling functions.

Fixes build issue.

collects/images/private/flomap.rkt

@@ -10,10 +10,25 @@
          "flomap-composite.rkt"
          "flomap-resize.rkt")
 
+;; This is a copy of the definition in typed/mred/mred
+;; but requiring that produces an error when building
+;; the docs
+(define-type Bitmap%
+  (Class (Real Real Boolean)
+         ()
+         ([get-width (-> Integer)]
+          [get-height (-> Integer)]
+          [get-argb-pixels
+           (case-> 
+            (Integer Integer Integer Integer Bytes Boolean
+                     -> Void)
+            (Integer Integer Integer Integer Bytes Boolean Boolean
+                     -> Void))])))
+
 (require/typed
  "flomap-convert.rkt"
- [bitmap->flomap  (Any -> flomap)]
- [flomap->bitmap  (flomap -> Any)]
+ [bitmap->flomap  ((Instance Bitmap%) -> flomap)]
+ [flomap->bitmap  (flomap -> (Instance Bitmap%))]
  [draw-flomap     ((Any -> Any) Integer Integer -> flomap)])
 
 (provide (all-from-out "flomap-struct.rkt"