stereo_mpi: Fix bug where num processes equal 1

It wasn't creating the links. Whoops.
core: Make interest points repeatable

This reinstates Oleg earlier work. However this time I doing it in ASP
so VW users don't have to take this overhead cost. I'm not sure why
this fixes the problem ... I still believe IP order shouldn't
matter. But RANSAC sampling would cause this problem.
core: Fix logic on IP filtering when altitude filtering is disabled

I had not that shouldn't have been there. This was causing all IP to
be filtered out in the event that the IP didn't have a good 2 normal
distribution of altitudes against datum. (such as when they're mostly
inliers or the outliers are just tricky).