(Necro|double)post warning

[Legend-of-iPhoenix]

Not sure how feasible this is, especially seeing that one can make a post on pages way earlier than the current page. Perhaps that deserves its own warning- "there are more recent pages in this thread" or something.

I'm generally strongly against barriers to posting, but if necroposting is bothering people I might consider adding it?

[Legend-of-iPhoenix]

It occurred to me recently that similar code could be used to encourage edits instead of double posting