Fix race condition in NewSessionTicket

If a NewSessionTicket is received by a multi-threaded client when
attempting to reuse a previous ticket then a race condition can occur
potentially leading to a double free of the ticket data.

CVE-2015-1791

This also fixes RT#3808 where a session ID is changed for a session already
in the client session cache. Since the session ID is the key to the cache
this breaks the cache access.

Parts of this patch were inspired by this Akamai change:
c0bf69a791

Reviewed-by: Rich Salz <rsalz@openssl.org>

include/openssl/ssl.h

@@ -2048,6 +2048,7 @@ void ERR_load_SSL_strings(void);
 # define SSL_F_SSL_READ                                   223
 # define SSL_F_SSL_SCAN_CLIENTHELLO_TLSEXT                320
 # define SSL_F_SSL_SCAN_SERVERHELLO_TLSEXT                321
+# define SSL_F_SSL_SESSION_DUP                            348
 # define SSL_F_SSL_SESSION_NEW                            189
 # define SSL_F_SSL_SESSION_PRINT_FP                       190
 # define SSL_F_SSL_SESSION_SET1_ID_CONTEXT                312