* sgen-cardtable.c (sgen_card_table_is_range_marked): Use
	card_in_range here since this is used for objects that can
	start at the middle of a card.

	* sgen-cardtable.c (move_cards_to_shadow_table): Properly
	copy the tail bytes of an object that spam around the cardtable.
	Don't copy more bytes than required.

	* sgen-cardtable.c (sgen_cardtable_scan_object): Add extra_idx
	variable that tracks the card offset that we're scanning. This
	is required when we wrap around.

	* sgen-cardtable.c (sgen_cardtable_scan_object): Properly reset
	card_base when at wrap around.