Unresolved reply visibility

[Gargron]

Solution: Instead of the reply? method being defined on the Status class from checking if in_reply_to_id was set, create reply as an explicit boolean field on the table. In before_validation, do the in_reply_to_id-based setting of it, unless it has already been set. In ProcessFeedService, set it to true explicitly when a thr:in-reply-to element is found.

Some filtering code may need to be adjusted for the case that thread is nil, and public timelines queries need to be adjusted to check reply = false instead of in_reply_to_id IS NULL. Anyway, the reason this will work is the following:

If, when a status comes in, the status it replies to is not in the system already, that means nobody on the system follows the user being replied to. The home feed filters out replies to people the user doesn't follow. Ergo, statuses for which it's known that it's a reply, but not known what is being replied to, can be filtered out straight away. This will fix lots of confusion about replies showing up on feeds sometimes.