Fix for BUG#15110: mysqldump --triggers: does not include DEFINER clause

There are two main idea of this fix:
  - introduce a common function for server and client to split user value
    (<user name>@<host name>) into user name and host name parts;
  - dump DEFINER clause in correct format in mysqldump.

include/my_user.h

@@ -0,0 +1,35 @@
+/* Copyright (C) 2005 MySQL 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
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+/*
+  This is a header for libraries containing functions used in both server and
+  only some of clients (but not in libmysql)...
+*/
+
+#ifndef _my_user_h_
+#define _my_user_h_
+
+#include <my_global.h>
+
+C_MODE_START
+
+void parse_user(const char *user_id_str, uint user_id_len,
+                char *user_name_str, uint *user_name_len,
+                char *host_name_str, uint *host_name_len);
+
+C_MODE_END
+
+#endif /* _my_user_h_ */