bug#28074: 25.2; `Info-toc' should not duplicate nodes by processing `The Detailed Node Listing'

[Drew Adams <drew.adams@oracle.com>]

emacs -Q
C-h i

Go to the Elisp manual or the Emacs manual.  Each of these has a menu of
nodes followed by a section called "The Detailed Node Listing".

M-x Info-toc

The result is not just a hierarchical TOC of the manual's nodes.  The
result duplicates both the menu (hierarchical) structure AND the flat,
"Detailed Node List".  The "Detailed Node List" lists each node multiple
times, once at the top level and once under each of its ancestor nodes.

This produces a TOC that is more than twice as big as it should be.  But
more importantly, the result of processing the "Detailed Node List" part
is an almost incomprehensible list of links, with a great deal of
redundancy.

For example, the node `A Sample Function Description' appears 4 times:

1. In the hierarchical menu listing, under `Format of Descriptions',
   which is under `Conventions', which is under `Introduction' (at the
   top level).

2. In the detailed listing, under `Format of Descriptions', which is
   under `Conventions' (at the top level).

3. In the detailed listing, under `Format of Descriptions' (at the top
   level).

4. In the detailed listing, at the top level.

Only the first of these occurrences of `A Sample Function Description'
is needed for a TOC.  And as you move further down the TOC entries and
their contexts become less readable.


In GNU Emacs 25.2.1 (x86_64-w64-mingw32)
 of 2017-04-24
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --without-dbus --without-compress-install 'CFLAGS=-O2
 -static -g3''