(Info-file-supports-index-cookies): New variable.

(Info-file-supports-index-cookies): New variable.
(Info-find-node-2): Check makeinfo version for index cookie support.
(Info-index-nodes): Search for nodes with index cookies only when
Info-file-supports-index-cookies is t.  Otherwise, search nodes
with "Index" in the node name.
(Info-index-node): Search index cookie in the current node only when
Info-file-supports-index-cookies is t.  Otherwise, check the word
"Index" in the node name.
(Info-find-emacs-command-nodes): Remove code that searches nodes
with "Index" node name in the top menu.