fix a redraw bug.  Things are faster but not fixed.

- Fix the real problem.  More cleanup of the cursor/selection code is required.
  There is too much incest in there.  We are redoing 75% of the necessary operations
  at several level in an attempt to get all the requisite pieces.

2000-02-20  Jody Goldberg <jgoldberg@home.com>

	* src/item-cursor.c : Switch to a quartic approved delayed update
	  model.  Do not change the bounding box while drawing.

	* src/selection.c (sheet_selection_add_range) : Do NOT directly change
	  the edit/move/base characteristics of the sheet sheet_cursor_set handles
	  that.

	* src/gnumeric-sheet.c (gnumeric_sheet_compute_visible_ranges) : Use
	  item_cursor_reposition rather than pretending that the cursor moved.

	* src/item-grid.c (item_grid_button_1) : Don't call both
	  sheet_cursor_move and sheet_selection_add.  The former was moving
	  the edit cursor without redrawing it.