1999-12-30  Jody Goldberg <jgoldberg@home.com>

	* src/file.c (workbook_load_from) : The 'open' functions return error
	  strings now.  Success == NULL, standard error == "", custom error
	  which needs to be freed is everything else.
	(workbook_try_read) : An optional argument in which to store error
	  messages returned by the loaders.
	(file_error_message) : Support the custom error messages.
	(workbook_read) : Ditto.

	* src/xml-io.c (xml_workbook_read) : Return simple error strings.