Add support for client side parsing of the PSK extension

Requires a refactor of the ServerHello parsing, so that we parse first and
then subsequently process. This is because the resumption information is
held in the extensions block which is parsed last - but we need to know that
information earlier.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2259)

ssl/ssl_err.c

diff --git a/ssl/ssl_err.c b/ssl/ssl_err.c
index 2186f79..9b02c58 100644
--- a/ssl/ssl_err.c
+++ b/ssl/ssl_err.c
@@ -373,6 +373,7 @@
      "tls_parse_ctos_renegotiate"},
     {ERR_FUNC(SSL_F_TLS_PARSE_CTOS_USE_SRTP), "tls_parse_ctos_use_srtp"},
     {ERR_FUNC(SSL_F_TLS_PARSE_STOC_KEY_SHARE), "tls_parse_stoc_key_share"},
+    {ERR_FUNC(SSL_F_TLS_PARSE_STOC_PSK), "tls_parse_stoc_psk"},
     {ERR_FUNC(SSL_F_TLS_PARSE_STOC_RENEGOTIATE),
      "tls_parse_stoc_renegotiate"},
     {ERR_FUNC(SSL_F_TLS_PARSE_STOC_USE_SRTP), "tls_parse_stoc_use_srtp"},
@@ -454,6 +455,7 @@
     {ERR_REASON(SSL_R_BAD_PACKET_LENGTH), "bad packet length"},
     {ERR_REASON(SSL_R_BAD_PROTOCOL_VERSION_NUMBER),
      "bad protocol version number"},
+    {ERR_REASON(SSL_R_BAD_PSK_IDENTITY), "bad psk identity"},
     {ERR_REASON(SSL_R_BAD_RECORD_TYPE), "bad record type"},
     {ERR_REASON(SSL_R_BAD_RSA_ENCRYPT), "bad rsa encrypt"},
     {ERR_REASON(SSL_R_BAD_SIGNATURE), "bad signature"},