add SSL_CONF functions and documentation (backport from HEAD)

ssl/ssl_lib.c

@@ -1168,6 +1168,20 @@ LHASH_OF(SSL_SESSION) *SSL_CTX_sessions(SSL_CTX *ctx)
 long SSL_CTX_ctrl(SSL_CTX *ctx,int cmd,long larg,void *parg)
 	{
 	long l;
+	/* For some cases with ctx == NULL perform syntax checks */
+	if (ctx == NULL)
+		{
+		switch (cmd)
+			{
+		case SSL_CTRL_SET_CURVES_LIST:
+			return tls1_set_curves_list(NULL, NULL, parg);
+		case SSL_CTRL_SET_SIGALGS_LIST:
+		case SSL_CTRL_SET_CLIENT_SIGALGS_LIST:
+			return tls1_set_sigalgs_list(NULL, parg, 0);
+		default:
+			return 0;
+			}
+		}
 
 	switch (cmd)
 		{