Examine nontrival dependencies using Homebrew #274
Description
In brief, we use homebrew to install open-mpi, which installs gfortran regardless of whether it is already installed. Because it's higher in the path, it takes precedence is used rather than the correct gfortran. We discussed possibly no longer install CRAN package Rmpi, which needs open-mpi, as well as reviewing other homebrew-dependent packages since homebrew does not currently respect versions or use existing packages on the machine to meet dependencies.