I hit a stumbling block today, and this is one of those things that really should be Googleable.
If you're installing libraries on a Mac, you might be doing it through Fink. And Fink has the unfortunate property that a lot of its download URLs give 404 errors, leaving you stuck. This was the case for the "cloog" library. I don't know what it does, but it's required by hdf5, which is needed by pytables, which we need to store Divisi results on the disk instead of in every instance of the Web server. All the URLs that Fink looks for when it tries to download "cloog" are broken.
The workaround is to Google for the file yourself, and download it into the /sw/src directory.
I hope this helps someone else who runs into the same problem.