Add negotiation of Extended Master Secret

(But not the actual thing yet.)
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 8ca83eb..d4cde0f 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -96,6 +96,7 @@
 #define DFL_TICKETS             SSL_SESSION_TICKETS_ENABLED
 #define DFL_ALPN_STRING         NULL
 #define DFL_FALLBACK            -1
+#define DFL_EXTENDED_MS         -1
 
 #define GET_REQUEST "GET %s HTTP/1.0\r\nExtra-header: "
 #define GET_REQUEST_END "\r\n\r\n"
@@ -134,6 +135,7 @@
     int tickets;                /* enable / disable session tickets         */
     const char *alpn_string;    /* ALPN supported protocols                 */
     int fallback;               /* is this a fallback connection?           */
+    char extended_ms;           /* negotiate extended master secret?        */
 } opt;
 
 static void my_debug( void *ctx, int level, const char *str )
@@ -293,6 +295,13 @@
 #define USAGE_FALLBACK ""
 #endif
 
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+#define USAGE_EMS \
+    "    extended_ms=0/1     default: (library default: on)\n"
+#else
+#define USAGE_EMS ""
+#endif
+
 #define USAGE \
     "\n usage: ssl_client2 param=<>...\n"                   \
     "\n acceptable parameters:\n"                           \
@@ -323,6 +332,7 @@
     USAGE_TRUNC_HMAC                                        \
     USAGE_ALPN                                              \
     USAGE_FALLBACK                                          \
+    USAGE_EMS                                               \
     "\n"                                                    \
     "    min_version=%%s      default: \"\" (ssl3)\n"       \
     "    max_version=%%s      default: \"\" (tls1_2)\n"     \
@@ -424,6 +434,7 @@
     opt.tickets             = DFL_TICKETS;
     opt.alpn_string         = DFL_ALPN_STRING;
     opt.fallback            = DFL_FALLBACK;
+    opt.extended_ms         = DFL_EXTENDED_MS;
 
     for( i = 1; i < argc; i++ )
     {
@@ -539,6 +550,15 @@
                 default: goto usage;
             }
         }
+        else if( strcmp( p, "extended_ms" ) == 0 )
+        {
+            switch( atoi( q ) )
+            {
+                case 0: opt.extended_ms = SSL_EXTENDED_MS_DISABLED; break;
+                case 1: opt.extended_ms = SSL_EXTENDED_MS_ENABLED; break;
+                default: goto usage;
+            }
+        }
         else if( strcmp( p, "min_version" ) == 0 )
         {
             if( strcmp( q, "ssl3" ) == 0 )
@@ -902,6 +922,11 @@
         }
 #endif
 
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+    if( opt.extended_ms != DFL_EXTENDED_MS )
+        ssl_set_extended_master_secret( &ssl, opt.extended_ms );
+#endif
+
 #if defined(POLARSSL_SSL_ALPN)
     if( opt.alpn_string != NULL )
         if( ( ret = ssl_set_alpn_protocols( &ssl, alpn_list ) ) != 0 )