Mac OS: make clear that image capture from screen returns an image in…

… premultiplied RGBA format (cont'd).

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@9725 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/Fl_cocoa.mm

@@ -3335,9 +3335,9 @@ void fl_mac_set_about( Fl_Callback *cb, void *user_data, int shortcut)
 }
 
 unsigned char *Fl_X::bitmap_from_window_rect(Fl_Window *win, int x, int y, int w, int h, int *bytesPerPixel)
-/* Returns a capture of part of a mapped window as a pre-multiplied RGBA array of bytes.
- At present, alpha values are always 1 (or 0 for the angles of a window title bar)
- because only opaque colors are used to draw, so pre-multiplication can be ignored. 
+/* Returns a capture of a rectangle of a mapped window as a pre-multiplied RGBA array of bytes.
+ Alpha values are always 1 (except for the angles of a window title bar)
+ so pre-multiplication can be ignored. 
  *bytesPerPixel is always set to the value 4 upon return.
  delete[] the returned pointer after use
  */