DB - allow private messages to expire
allow private mail sender to set an expiration on their messages. Once expired the message is destroyed at both ends (subject to the granularity of the polling interval) and is gone. Officially it takes some form of language independent string like 2013/11/22, but English speakers can use anything that strtotime() understands, like "+30 minutes" or "next Tuesday".
Merge https://github.com/friendica/red into zpull