2003-08-16  Jody Goldberg <jody@gnome.org>

	A bit of tidying to make 70184 simpler
	* src/cell.c (cell_is_empty) : renamed from cell_is_blank.  All
	  callers changed.
	(cell_is_blank) : new function that handles "" too.

	* src/sheet-filter.c (cb_collect_unique) : Use it here.
	(cb_filter_non_blanks) : here.
	(cb_filter_blanks) : and here.