Add pointer to Fl_Image::scale() to documentation of Fl_Image::copy(int, int)

src/Fl_Image.cxx

@@ -80,6 +80,10 @@ void Fl_Image::draw_empty(int X, int Y) {
 /**
   Creates a resized copy of the image.
 
+  It is recommended not to call this member function to reduce the size
+  of an image to the size of the area where this image will be drawn,
+  and to use Fl_Image::scale() instead.
+ 
   The new image should be released when you are done with it.
 
   Note: since FLTK 1.4.0 you can use Fl_Image::release() for all types