WordPress:WPMU Functions/wpmu validate user signup

Make some verifications about Username and Email.
Localize : ''wp-includes\wpmu-functions.php

Username validation

• If not empty
• If not illegal names like :
  "www", "web", "root", "admin", "main", "invite", "administrator"
• Number of letters, at least 4 characters
• If is not contain "underscore", the _ character
• If is not only contain number
• If the username already exists in DB

Email validation

• If not listed like bad/unsafe email adress
• If is a valid email : x@x.xx
• If is the validation done
• If the email already exists in DB