fixed irradiation loader tests. use get_data_dir for all path operations
fixed irradiation loader tests. use get_data_dir for all path operations

USGSDenverPychron/pychron,UManPychron/pychron,USGSDenverPychron/pychron,NMGRL/pychron,NMGRL/pychron,UManPychron/pychron,NMGRL/pychron,UManPychron/pychron,USGSDenverPychron/pychron,USGSDenverPychron/pychron,UManPychron/pychron,NMGRL/pychron