don't use my_copystat in the server

it was supposed to be used in command-line tools only.
Different fix for 4e54738:

Bug#24388746: PRIVILEGE ESCALATION AND RACE CONDITION USING CREATE TABLE

Author: vuvova

include/my_sys.h

@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2013, Oracle and/or its affiliates.
-   Copyright (c) 2010, 2013, Monty Program Ab.
+   Copyright (c) 2010, 2016, Monty Program Ab.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -246,7 +246,7 @@ extern my_bool my_use_symdir;
 extern ulong	my_default_record_cache_size;
 extern my_bool  my_disable_locking, my_disable_async_io,
                 my_disable_flush_key_blocks, my_disable_symlinks;
-extern my_bool my_disable_sync;
+extern my_bool my_disable_sync, my_disable_copystat_in_redel;
 extern char	wild_many,wild_one,wild_prefix;
 extern const char *charsets_dir;
 /* from default.c */

mysys/my_redel.c

@@ -1,5 +1,5 @@
-/*
-   Copyright (c) 2000, 2010, Oracle and/or its affiliates
+/* Copyright (c) 2000, 2010, Oracle and/or its affiliates
+   Copyright (c) 2009, 2016, MariaDB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -49,7 +49,8 @@ int my_redel(const char *org_name, const char *tmp_name,
   DBUG_PRINT("my",("org_name: '%s' tmp_name: '%s'  MyFlags: %d",
 		   org_name,tmp_name,MyFlags));
 
-  if (my_copystat(org_name,tmp_name,MyFlags) < 0)
+  if (!my_disable_copystat_in_redel &&
+      my_copystat(org_name,tmp_name,MyFlags) < 0)
     goto end;
   if (MyFlags & MY_REDEL_MAKE_BACKUP)
   {

mysys/my_static.c

@@ -99,6 +99,7 @@ my_bool my_disable_sync=0;
 my_bool my_disable_async_io=0;
 my_bool my_disable_flush_key_blocks=0;
 my_bool my_disable_symlinks=0;
+my_bool my_disable_copystat_in_redel=0;
 
 /*
   Note that PSI_hook and PSI_server are unconditionally

sql/mysqld.cc

@@ -3455,6 +3455,7 @@ static int init_common_variables()
 
   max_system_variables.pseudo_thread_id= (ulong)~0;
   server_start_time= flush_status_time= my_time(0);
+  my_disable_copystat_in_redel= 1;
 
   rpl_filter= new Rpl_filter;
   binlog_filter= new Rpl_filter;