(Info-streamline-headings): New var.

(Info-streamline-headings): New var.
(Info-dir-remove-duplicates): New fun.
(Info-insert-dir): Use it.  Simplify the code with push,mapc,dolist.
(Info-select-node): Simplify handling of Info-header-line.
(Info-forward-node): Undo 2000/12/15 since we don't narrow any more.
(Info-mode): Set header-line-format once and for all.
(Info-fontify-node): Accept bogus first line with `File:' missing.
Only make first line invisible if Info-use-header-line.
Don't use `intangible': it's evil.  Use inhibit-read-only.
(Info-follow-reference, Info-next-reference, Info-prev-reference)
(Info-try-follow-nearest-node): Don't bind inhibit-point-motion-hooks
since we don't use intangible any more.