Save user - huge data

When saving a user, variables are stored in the database field users.data. Currently, user_edit_submit fails to remove certain form fields, most importantly "_account", which is a copy of the whole array. Repeatedly editing an account lets the size of the database record go up exponentially.

Try "SELECT uid,name,LENGTH(data) FROM users" (for MySQL), then go to my account -> edit & submit, then look again. Any difference?

Possible fix: remove those fields from $form_values - see patch.