Add option for relaxed X509 time verification.

The certificates are not valid according to the RFC, but are in wide
distribution across the internet. Hence the request to add a
compile-time flag to accept these certificates if wanted by the
application.

If POLARSSL_RELAXED_X509_DATE is enabled it will allow dates without
seconds, and allow dates with timezones (but doesn't actually use
the timezone).

Patch provided by OpenVPN.
diff --git a/include/polarssl/config.h b/include/polarssl/config.h
index 8fdf36e..4e52790 100644
--- a/include/polarssl/config.h
+++ b/include/polarssl/config.h
@@ -1177,6 +1177,17 @@
 //#define POLARSSL_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION
 
 /**
+ * \def POLARSSL_X509_ALLOW_RELAXED_DATE
+ *
+ * If set, the X509 parser will not break-off when parsing an X509 certificate
+ * and encountering ASN.1 UTCTime or ASN.1 GeneralizedTime without seconds or
+ * with a time zone.
+ *
+ * Uncomment to prevent an error.
+ */
+//#define POLARSSL_X509_ALLOW_RELAXED_DATE
+
+/**
  * \def POLARSSL_X509_CHECK_KEY_USAGE
  *
  * Enable verification of the keyUsage extension (CA and leaf certificates).