rem: WMFindInBag(WMBag *self, int (*match)(void*,void*), void *cdata)
add: WMFindInBag(WMBag *self, WMMatchDataProc *match, void *cdata)
context: WMFindInBag(WMBag *self, int (*match)(void*,void*), void *cdata){    return findInTree(self, self->root, match, cdata);}