Add merged cell support to autofill.

2000-12-29  Jody Goldberg <jgoldberg@home.com>

	* src/sheet-autofill.c (sheet_autofill_dir) : support merged cells.
	(fill_item_new) : Ditto.

	* src/sheet.c
	(sheet_merge_add) : rename
	(sheet_merge_remove) : rename
	(sheet_merge_get_overlap) : rename
	(sheet_merge_contains_pos) : rename
	(sheet_merge_is_corner) : rename
	(sheet_merged_relocate) : rename
	(sheet_merge_get_adjacent) : rename

	* src/rendered-value.c (rendered_value_new) : Use
	  sheet_merge_is_corner rather than sheet_region_get_merged_cell.