[PATCH] mysql_upgrade breaks databases with long user names

mysql_upgrade is supposed to be a no-op on databases that are fully upgraded already. But scripts/mysql_system_tables_fix.sql has lots of old statements including those that try to modify User column in different tables to be char(16) instead of char(80). That breaks databases that already have users with names longer than 16 characters.

In the attachment is a patch that fixes the problem (with a test).