tests: added several invalid certificates

Provided by Pascal Cuoq.

tests/decoding-invalid-x509

diff --git a/tests/decoding-invalid-x509 b/tests/decoding-invalid-x509
index 3f66bb0..01d9cb0 100755
--- a/tests/decoding-invalid-x509
+++ b/tests/decoding-invalid-x509
@@ -29,8 +29,9 @@
 
 for i in "${srcdir}/invalid-x509/"*.der;do
 $VALGRIND $ASN1DECODING "$ASN1PKIX" "$i" PKIX1.Certificate >/dev/null 2>&1
-if test $? != 1;then
-	echo "Decoding failed"
+ret=$?
+if test $ret != 1;then
+	echo "Decoding failed for $i"
 	exit 1
 fi
 echo "$(basename $i): ok"