Fixes for upside-down DIBs.

diff --git a/include/bitmap.h b/include/bitmap.h
index f7a8902..45399a3 100644
--- a/include/bitmap.h
+++ b/include/bitmap.h
@@ -55,6 +55,7 @@
 
   /* objects/dib.c */
 extern int DIB_GetDIBWidthBytes( int width, int depth );
+extern int DIB_GetDIBImageBytes( int width, int height, int depth );
 extern int DIB_BitmapInfoSize( BITMAPINFO * info, WORD coloruse );
 extern int DIB_GetBitmapInfo( const BITMAPINFOHEADER *header, DWORD *width,
                               int *height, WORD *bpp, WORD *compr );