* info.el (Info-directory-list): Doc fix; it is set according to

* info.el (Info-directory-list): Doc fix; it is set according to
	INFOPATH, not INFODIR.
	(Info-find-node): Don't try to set the info buffer's directory
	according to Info-directory; that variable doesn't exist any more.
	Instead, let Info-insert-dir set the current directory.
	(Info-insert-dir): Properly check for upper- and lower-case forms
	of "dir", with and without ".info" extension.  Set the buffer's
	default-directory to the directory containing the first dir file
	we find, and cache it in Info-dir-contents-directory.
	(Info-dir-contents-directory): New variable, to cache the
	directory we decided to use as the merged directory's
	default-directory.