[devel] Addressed various issues identified by GCC, mostly signed/unsigned

and shortening problems on assignment but also a few difficult to optimize
(for GCC) loops (John Bowler).
diff --git a/pngpriv.h b/pngpriv.h
index a3b0dc3..c46375c 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -1188,7 +1188,7 @@
 PNG_EXTERN png_byte png_gamma_8bit_correct PNGARG((unsigned int value,
     png_fixed_point gamma));
 PNG_EXTERN void png_build_gamma_table PNGARG((png_structp png_ptr,
-    png_byte bit_depth));
+    int bit_depth));
 #endif
 
 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */