EntityStorageException: The username and email are both addresses that do not match. (But what are they?)

Description of the need

Found this PHP error in watchdog on a site, resulting from a cron run:

EntityStorageException: The username and email are both addresses that do not match. in EntityDatabaseStorageController->save() (line 789 of /.../core/modules/entity/entity.controller.inc).

Yes, OK, but which entity of the several thousand users are we talking about here? And what's the mismatch?

Proposed solution

It would be nice to add to the error message the actual username and email to make it easier to track down what's wrong. (In this case, one was capitalized, the other wasn't.)

The message is generated at line 368 of user.entity.inc, currently:

        throw new EntityMalformedException'The username and email are both addresses that do not match.');

I propose we change this to

        throw new EntityMalformedException(format_string('The username @name and email @mail are both addresses that do not match.', array('@name' => $entity->name, '@mail' => $entity->mail)));

This isn't technically a bug, but it seems simple enough that it could go into a bugfix release.