Among others, add a remapping for C-x 4 d, cf. Bug#26360.

* lisp/ido.el (ido-mode): Remap missing commands.
(ido-file-internal, ido-visit-buffer): Add support for new
methods.
(ido-display-buffer-other-frame)
(ido-find-alternate-file-other-window, ido-dired-other-window)
(ido-dired-other-frame): New commands.

* test/lisp/ido-tests.el (ido-tests--other-window-frame): Add unit
test for the bindings.

* lisp/info.el (Info-complete-menu-item): Add `category' metadata.
(Info-menu): Simplify now that we use the `default' arg of completing-read.
* lisp/minibuffer.el (completion-category-defaults): Use substring
completion for `info-menu`.

These changes also make use of touchpad and trackpad (Bug#26347).

* doc/emacs/frames.texi (Mouse Commands): Document horizontal
scrolling using the mouse wheel.

* lisp/mwheel.el (mwheel-scroll): Respond to wheel-right and wheel-left.
(mwheel-tilt-scroll-p, mwheel-flip-direction)
(mwheel-scroll-left-function, mwheel-scroll-right-function): New
defcustoms.
(mouse-wheel-left-event, mouse-wheel-right-event): New variables,
events that calls wheel-left/right.

* etc/NEWS: Mention horizontal scrolling using the mouse wheel.

* lisp/emacs-lisp/package.el (package-import-keyring)
(package--check-signature-content, package-check-signature):
Use new variable package-gnupghome-dir to control which GnuPG
homedir to use.
* doc/emacs/package.texi: Mention package-gnupghome-dir.
* etc/NEWS: Mention package-gnupghome-dir.

* doc/misc/tramp.texi (Change file name syntax): New node.

* etc/NEWS: Mention `tramp-change-syntax'.

* lisp/net/tramp.el (tramp-file-name-regexp): Reinsert it.
External packages uses it.
(tramp-syntax): Set also `tramp-file-name-regexp'.

Since copy-sequence seems to be needed anyway for records, have it
work on records, and remove copy-record as being superfluous.
* doc/lispref/records.texi (Records, Record Functions):
* lisp/emacs-lisp/cl-macs.el (cl-defstruct):
* lisp/emacs-lisp/eieio.el (make-instance, clone):
* test/src/alloc-tests.el (record-3):
Use copy-sequence, not copy-record, to copy records.
* doc/lispref/sequences.texi (Sequence Functions)
(Array Functions): Document that aref and copy-sequence
work on records.
* etc/NEWS: Omit copy-record.
* src/alloc.c (Fcopy_record): Remove.
* src/data.c (Faref): Document that arg can be a record.
* src/fns.c (Fcopy_sequence): Copy records, too.

* fileio.c (write_region):
* epa-file.el (epa-file-write-region):
* jka-compr.el (jka-compr-write-region):
* ange-ftp.el (ange-ftp-write-region):
* tramp-gvfs.el (tramp-gvfs-handle-write-region):
* tramp-sh.el (tramp-sh-handle-write-region):
* mm-util.el (mm-append-to-file): Functions now output
characters written in addition to file name.
* files.texi: Added documentation to write-region and
append-to-file describing their output.

In Greek, a sigma character has two lower case forms which depend on
their position in the word.  Implement logic determining it.

* src/casefiddle.c (struct casing_context, case_character_impl): Don’t
assume inword is true when flag is CASE_UP and false when flag is
CASE_DOWN.  For final sigma detection we need this information tracked
reliably;.
(CAPITAL_SIGMA, SMALL_SIGMA, SMALL_FINAL_SIGMA): New macros defining
Unicode code point of different forms of sigma letter.
(case_character): Implement support for final sigma casing.
(do_casify_multibyte_string, do_casify_multibyte_region): Update after
changes to case_character.

* test/src/casefiddle-tests.el (casefiddle-tests-casing): Add test
cases for final sigma.