Vacuum/visibility is busted

While stress testing Pavan's 2nd pass vacuum visibility patch, I realized
that vacuum/visibility was busted. But it wasn't his patch that busted it.
As far as I can tell, the bad commit was in the
range 692079e5dcb331..168d3157032879

Since a run takes 12 to 24 hours, it will take a while to refine that
interval.

I was testing using the framework explained here:

http://www.postgresql.org/message-id/CAMkU=1xoA6Fdyoj_4fMLqpicZR1V9GP7cLnXJdHU+iGgqb6WUw@mail.gmail.com

Except that I increased JJ_torn_page to 8000, so that autovacuum has a
chance to run to completion before each crash; and I turned off
archive_mode as it was not relevant and caused annoying noise. As far as I
know, crashing is entirely irrelevant to the current problem, but I just
used and adapted the framework I had at hand.

A tarball of the data directory is available below, for those who would
like to do a forensic inspection. The table jjanes.public.foo is clearly
in violation of its unique index.

https://docs.google.com/file/d/0Bzqrh1SO9FcEbk1lUWgwSk9Od28/edit?usp=sharing

Thanks for any help,

Jeff