windows: added a traceback attribute to Callback objects for debugging
windows: added a traceback attribute to Callback objects for debugging

juggernate/pymel,juggernate/pymel,assumptionsoup/pymel,AtonLerin/pymel,david-lassonde-adsk/pymel,shrtcww/pymel,AtonLerin/pymel,david-lassonde-adsk/pymel,leonsooi/pymel,shrtcww/pymel,leonsooi/pymel,cgrebeld/pymel,assumptionsoup/pymel