bug#29839: 26.0; Bad xrefs in (elisp) `Sequence Functions'

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

There are two links in node `Sequence Functions' that are labeled
`Definition of nth'.  The context suggests that by following them you
find information about `aref' and `nth'.  But they take you instead to
node `Building Lists', which does not mention either `aref' or `nth' and
does not seem to help with the origin context.

The only occurrence of "Nth" in that node describes how "The Nth element
of the list is computed", where the list is what is returned by
`number-sequence'.  This not only doesn't help in this context; it
confuses.

This is a regression introduced in Emacs 24.  In Emacs 23 those links
take you to the description of function `nth' in node `List Elements'.

In GNU Emacs 26.0.90 (build 3, x86_64-w64-mingw32)
 of 2017-10-13
Repository revision: 906224eba147bdfc0514090064e8e8f53160f1d4
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''