(Info-toc): Call Info-mode on intermediate buffer.

(Info-toc): Call Info-mode on intermediate buffer.
(Info-index-nodes): Enclose code in condition-case to catch errors.
(Info-index-node): Don't search all index nodes if request is only
for the current node and file is not in the cache of index nodes.
(Info-mode-map): Bind Info-copy-current-node-name to `w'
for consistency with dired-copy-filename-as-kill.
Bind `S' to Info-search-case-sensitively.
(Info-copy-current-node-name): New arg.  With zero prefix arg put
the name inside a function call to `info'.  Display copied text in
the echo area.