Update libpng to version 1.6.3

Change-Id: I86cb46ec376eb41324b82d2875757aeda734c5c1
diff --git a/tests/pngstest-3p02 b/tests/pngstest-3p02
new file mode 100755
index 0000000..770a75c
--- /dev/null
+++ b/tests/pngstest-3p02
@@ -0,0 +1,2 @@
+#!/bin/sh
+exec "${srcdir}/tests/pngstest" 3p02