Port project-release-serve-history.php to D6

While working on #375823: Move updates.d.o to its own webroot I realized that we never actually ported project-release-serve-history.php itself to D6. There are two main things to change:

A) We need to set $_SERVER['HTTP_HOST'] = SITE_NAME; and define SITE_NAME so the bootstrapping works. Not sure how this even works in D5, to be honest. ;)

B) In D6, ip_address() is always available, so we can avoid checking for it.

I'm on it... stay tuned.