-machinefile support

[Christopher D. Maestas]

I don't know if it's in the todo list, but is it possible to have mpiexec include a "-machinefile " option?
People grab a set of nodes, then launch executables on different sets of nodes with different machinefiles.
I explained how to do it with the -conf option, but was wondering if the -machinefile option could be used,
then the testers don't have to change nothing in their suite.

-- Chris