Override dict.copy method on AttributeDict
Override dict.copy method on AttributeDict

The copy implementation of dict always returns a dict instead of copying the
current dict subclass.

GraylinKim/sc2reader,ggtracker/sc2reader,ggtracker/sc2reader,GraylinKim/sc2reader,vlaufer/sc2reader,dsjoerg/sc2reader,vlaufer/sc2reader,StoicLoofah/sc2reader,StoicLoofah/sc2reader,dsjoerg/sc2reader