CURLOPT_PINNEDPUBLICKEY.3: mention error code

docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -37,6 +37,8 @@ When negotiating a TLS or SSL connection, the server sends a certificate
 indicating its identity. A public key is extracted from this certificate and
 if it does not exactly match the public key provided to this option, curl will
 abort the connection before sending or receiving any data.
+
+On mismatch, \fICURLE_SSL_PINNEDPUBKEYNOTMATCH\fP is returned.
 .SH DEFAULT
 NULL
 .SH PROTOCOLS