refactored: pymel to pymel.core for pre-2009 MEL-based plugin loaded callbacks
refactored: pymel to pymel.core for pre-2009 MEL-based plugin loaded callbacks

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