Post OSDI Merge

I merged the stuff in graphlabapi+mpi (which I think has most of the stuff Jacob and I were using for OSDI) into this "post-osdi" branch.

I've also done most of the porting of Alex's SSSP code.

Making this PR now because I don't have time to finish verifying that everything is okay, and didn't want to push to master until I had looked things over more thoroughly. Timeline is probably around Monday that I'll get back to this. If anyone else wants to take a crack, be my guest.