* info.el (Info-on-current-buffer): Record actual filename in

* info.el (Info-on-current-buffer): Record actual filename in
	Info-current-file, instead of t, or a fake filename if a non-file
	buffer.  Make autoload.
	(Info-find-node, Info-revert-find-node): No need to check for
	Info-current-file nil.
	(Info-set-mode-line, Info-up, Info-copy-current-node-name):
	Info-current-file is now never `t'.
	(Info-fontify-node): Many simplifications due to Info-current-file
	always being valid.  Use Info-find-file to find node filename.