Update libpng to version 1.6.3

Change-Id: I86cb46ec376eb41324b82d2875757aeda734c5c1
diff --git a/tests/pngstest-2c08 b/tests/pngstest-2c08
new file mode 100755
index 0000000..9e0de6f
--- /dev/null
+++ b/tests/pngstest-2c08
@@ -0,0 +1,2 @@
+#!/bin/sh
+exec "${srcdir}/tests/pngstest" 2c08