bug#47073: 28.0.50; speedbar: sorting in sublists is in reverse

[Harald Jörg]

This isn't specific for "current" Emacs, it happens in Emacs 26.1, too.

How to reproduce:

 - emacs -Q
 - open a Perl file with lots of subroutines
   (e.g. https://github.com/foswiki/distro/blob/master/core/lib/Foswiki.pm)
   or a Elisp file with lots of defuns
   (e.g. lisp/progmodes/cperl-mode.el)
 - M-x speedbar

Following the default configuration, speedbar clusters the display of
subroutines into alphabetically sorted batches of 20 entries each.

While the batches are sorted alphabetically (e.g. "ge to i" comes before
"l to re" in Foswiki.pm), the entries in each of the batches are sorted
in reverse: The batch "ge to i" has a first entry of "isValidWikiWord"
and a last entry of "getApproxRevTime".

This happens in both perl-mode _and_ cperl-mode, and only in speedbar
but not in the completion list after M-x imenu, nor in the imenu index
which I added with M-x imenu-add-menubar-index.  So, either the bug is
in speedbar - or both Perl modes share the same bug.

...And, as I just found out, it isn't specific for Perl files so, I've
modified the recipe above and can add:

The situation with large elisp files (e.g. lisp/progmodes/cperl-mode.el)
might give a clue what's happening to someone who is familiar with
speedbar:

 - batches with a single word headline (e.g. "cperl-e") are sorted
   according to the positions of the entries.

 - batches with a range in the headline (e.g. "cperl-auto to cperl-d")
   have their sub-entries sorted in reverse alphabetical order.

Cheers,
haj

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2021-03-02 built on hajtower
Repository revision: 9ef8a3bfca192777e7cf8b4748d188249a517582
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured features:
GIF GMP GNUTLS JPEG LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SOUND
THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM LUCID ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Info

Minor modes in effect:
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  mouse-wheel-mode: t
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  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/home/haj/devel/emacs-lisp/cperl-mode/cperl-mode hides 
/home/haj/devel/emacs/emacs/lisp/progmodes/cperl-mode

Features:
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