Background: T17294#9560358

Per the above task we currently does not even has reliable way to know whether a temporary account is expired.

Usecases:

• When user try to communiate with expired accounts, they should know the temporary account will not receive the message.
• When admin try to block expired temporary accounts, they should know such block will have no effect.
• They can be excluded from MassMessage.
• Twinkle and other 3rd tools can skip user talk page notifications of expired temporary users.