Print unparseable SubjectAlternativeNames

In x509_info_subject_alt_name() we silently dropped names that we
couldn't parse because they are not supported or are malformed. (Being
malformed might mean damaged file, but can be a sign of incompatibility
between applications.)

This commit adds code notifying the user that there is something, but
we can't parse it.
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index d3afe1f..99dd083 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -124,7 +124,7 @@
 
 X509 Certificate information, Subject Alt Name + Key Usage
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA1_C
-x509_cert_info:"data_files/cert_example_multi_nocn.crt":"cert. version     \: 3\nserial number     \: F7\:C6\:7F\:F8\:E9\:A9\:63\:F9\nissuer name       \: C=NL\nsubject name      \: C=NL\nissued  on        \: 2014-01-22 10\:04\:33\nexpires on        \: 2024-01-22 10\:04\:33\nsigned using      \: RSA with SHA1\nRSA key size      \: 1024 bits\nbasic constraints \: CA=false\nsubject alt name  \:\n    dNSName \: www.shotokan-braunschweig.de\n    dNSName \: www.massimo-abate.eu\nkey usage         \: Digital Signature, Non Repudiation, Key Encipherment\n"
+x509_cert_info:"data_files/cert_example_multi_nocn.crt":"cert. version     \: 3\nserial number     \: F7\:C6\:7F\:F8\:E9\:A9\:63\:F9\nissuer name       \: C=NL\nsubject name      \: C=NL\nissued  on        \: 2014-01-22 10\:04\:33\nexpires on        \: 2024-01-22 10\:04\:33\nsigned using      \: RSA with SHA1\nRSA key size      \: 1024 bits\nbasic constraints \: CA=false\nsubject alt name  \:\n    dNSName \: www.shotokan-braunschweig.de\n    dNSName \: www.massimo-abate.eu\n    <unsupported>\n    <unsupported>\nkey usage         \: Digital Signature, Non Repudiation, Key Encipherment\n"
 
 X509 Certificate information, RSA Certificate Policy any
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
@@ -172,7 +172,7 @@
 
 X509 Certificate information Bitstring in subject name
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA1_C
-x509_cert_info:"data_files/bitstring-in-dn.pem":"cert. version     \: 3\nserial number     \: 02\nissuer name       \: CN=Test CA 01, ST=Ecnivorp, C=XX, emailAddress=tca@example.com, O=Test CA Authority\nsubject name      \: C=XX, O=tca, ST=Ecnivorp, OU=TCA, CN=Client, emailAddress=client@example.com, serialNumber=7101012255, uniqueIdentifier=?7101012255\nissued  on        \: 2015-03-11 12\:06\:51\nexpires on        \: 2025-03-08 12\:06\:51\nsigned using      \: RSA with SHA1\nRSA key size      \: 2048 bits\nbasic constraints \: CA=false\nsubject alt name  \:\next key usage     \: TLS Web Client Authentication\n"
+x509_cert_info:"data_files/bitstring-in-dn.pem":"cert. version     \: 3\nserial number     \: 02\nissuer name       \: CN=Test CA 01, ST=Ecnivorp, C=XX, emailAddress=tca@example.com, O=Test CA Authority\nsubject name      \: C=XX, O=tca, ST=Ecnivorp, OU=TCA, CN=Client, emailAddress=client@example.com, serialNumber=7101012255, uniqueIdentifier=?7101012255\nissued  on        \: 2015-03-11 12\:06\:51\nexpires on        \: 2025-03-08 12\:06\:51\nsigned using      \: RSA with SHA1\nRSA key size      \: 2048 bits\nbasic constraints \: CA=false\nsubject alt name  \:\n    <unsupported>\next key usage     \: TLS Web Client Authentication\n"
 
 X509 certificate v1 with extension
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3:MBEDTLS_SHA1_C