Bug #43290 Remove the mysql anonymous user

Description:
In authenticating a user connecting to the server, there is a chance that they may match the "anonymous user" before matching their own user.

I'm requesting that this functionality be disabled in an upcoming release - since it causes more headaches for users than problems it solves.

How to repeat:
mysql> SELECT USER(), CURRENT_USER();
+-----------------+----------------+
| USER()          | CURRENT_USER() |
+-----------------+----------------+
| user1@localhost | @localhost     | 
+-----------------+----------------+

Note the empty current user.
See also: http://dev.mysql.com/doc/refman/5.1/en/account-activity-auditing.html

Suggested fix:
I don't want this fixed via an SQL mode preventing creation of an empty user.  I think it's more important for forward compatibility that the empty rows can still be present in the table, but are ignored.

This change in behavior should be enabled by default (incompatible change) unless a server option (such as --i-want-it-oldskool) is enabled at startup.

Thank you for the reasonable feature request.

This FR can be closed (5.7 sufficiently solves this).