Enable MPI in packaged builds
Remove requirement on CMake 2.8

Bring in FindMPI.cmake from a recent version of CMake so that the minimum requirement for the system cmake can be dropped back to 2.6
Fix the imported FindMPI so that it works
Add default search for openmpi

openmpi is installed in /usr/lib64/openmpi on some distros
Update install guide for 1.0