windows: for versions >= 2009, use open/close undo chunks instead of mel hack to ensure that an entire callback can be undone in one go. fixed a bug that was preventing non-ui functions from being created.
windows: for versions >= 2009, use open/close undo chunks instead of mel hack to ensure that an entire callback can be undone in one go. fixed a bug that was preventing non-ui functions from being created.

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