Deprecate some non-PK compatibility functions

(Should have been deprecated in 1.3.0 already.)
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 2e33ffd..c1aff67 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -1059,6 +1059,9 @@
  *                 up your certificate chain. The top certificate (self-signed)
  *                 can be omitted.
  *
+ * \warning        This backwards-compatibility function is deprecated!
+ *                 Please use \c ssl_set_own_cert() instead.
+ *
  * \param ssl      SSL context
  * \param own_cert own public certificate chain
  * \param rsa_key  own private RSA key
@@ -1081,6 +1084,10 @@
  *                 up your certificate chain. The top certificate (self-signed)
  *                 can be omitted.
  *
+ * \warning        This backwards-compatibility function is deprecated!
+ *                 Please use \c pk_init_ctx_rsa_alt()
+ *                 and \c ssl_set_own_cert() instead.
+ *
  * \param ssl      SSL context
  * \param own_cert own public certificate chain
  * \param rsa_key  alternate implementation private RSA key