Ensure s_client and s_server work when read_ahead is set

Previously s_client and s_server relied on using SSL_pending() which does
not take into account read_ahead. For read pipelining to work, read_ahead
gets set automatically. Therefore s_client and s_server have been
converted to use SSL_has_pending() instead.

Reviewed-by: Tim Hudson <tjh@openssl.org>

apps/s_client.c

@@ -2183,7 +2183,7 @@ int s_client_main(int argc, char **argv)
             }
         }
 
-        ssl_pending = read_ssl && SSL_pending(con);
+        ssl_pending = read_ssl && SSL_has_pending(con);
 
         if (!ssl_pending) {
 #if !defined(OPENSSL_SYS_WINDOWS) && !defined(OPENSSL_SYS_MSDOS) && !defined(OPENSSL_SYS_NETWARE)