Process signature algorithms during TLS v1.2 client authentication.

Make sure message is long enough for signature algorithms.

(backport from HEAD).

ssl/ssl.h

@@ -2357,6 +2357,7 @@ void ERR_load_SSL_strings(void);
 #define SSL_R_SERVERHELLO_TLSEXT			 275
 #define SSL_R_SESSION_ID_CONTEXT_UNINITIALIZED		 277
 #define SSL_R_SHORT_READ				 219
+#define SSL_R_SIGNATURE_ALGORITHMS_ERROR		 359
 #define SSL_R_SIGNATURE_FOR_NON_SIGNING_CERTIFICATE	 220
 #define SSL_R_SRP_A_CALC				 354
 #define SSL_R_SSL23_DOING_SESSION_ID_REUSE		 221