I cannot access http://community.invisionpower.com/topic/375454-my-site-redirecting-to-url4short/page-2?hl=url4short.net Avast is blocking it

As it should. That post contains malicious code that a user found on his forum.

Curious, wouldn't it be better to delete page 2

No - it's a reference support topic that may benefit others. :) The code cannot be executed and is safe. Avast is just being cautious, again, as it should.