Redirect to the last page after creating a new post in a forum thread

[cvzi]

If you post a reply post in a forum thread and that post creates a new page, then you should be redirected to the last page, where your new post is.

I found that I was not redirected to the last page and I was looking for my new post and couldn't find it, until I noticed that there was a newly generated second page.

[Martii]

That possibly won't be reliable depending on how #601 comes through. I do miss @sizzlemctwizzle 's original reverse order (LIFO) but that also will break some features with linking comments and such.... which is why I didn't put it back in after @Zren took it out on the bootstrap migration.

I'll tack this on to that milestone but my first instinct is a might fix.