Added error message for when execution of OOMMF fails
Added error message for when execution of OOMMF fails

ryanpepper/oommf-python,fangohr/oommf-python,ryanpepper/oommf-python,fangohr/oommf-python,ryanpepper/oommf-python,fangohr/oommf-python,ryanpepper/oommf-python