2001-08-28  Morten Welinder  <terra@diku.dk>

	* src/workbook.h (struct _Workbook): point to first dependent
 	directly, not via an slist.

	* src/eval.h (struct _Dependent): Add prev and next fields.

	* src/eval.c (dependent_unlink, dependent_unlink_sheet): Fix-up
 	unlinking.
	(dependent_link): Link using new double-linked structure.
	(sheet_region_queue_recalc): Use new dependent linking structure.
	(workbook_queue_all_recalc): Make an slist of dependents here.

	* src/workbook-control-gui.c (TOGGLE_HANDLER/display_formulas):
 	Adapt to new dependent linking structure.

	* src/workbook.c (workbook_expr_relocate): Adapt to new dependent
 	linking structure.