For discussion, see the following thread:
https://lists.gnu.org/r/emacs-devel/2020-04/msg00880.html
* doc/emacs/cmdargs.texi (General Variables): Mention
shell-file-name in relation to SHELL.
* doc/emacs/misc.texi (Interactive Shell): Move index entry for
SHELL environment variable from here, where it is not mentioned...
(Single Shell): ...to here, where it is discussed along with
shell-file-name.
* lisp/dired.el (dired-insert-directory): Use shell-file-name
instead of explicit-shell-file-name when a shell is implicitly
requested.
* lisp/obsolete/terminal.el (explicit-shell-file-name):
* lisp/term.el (explicit-shell-file-name): Remove duplicate
defcustoms and load lisp/shell.el instead. (Bug#40679)
* lisp/shell.el (explicit-shell-file-name): Clarify docstring.
(shell): Simplify.
Restore lines saying "Maintainer: emacs-devel@gnu.org" when there is
no special maintainer for a file. Although this wasn't documented
it was common practice and removing the lines didn't have consensus.
Most of this change is to boilerplate commentary such as license URLs.
This change was prompted by ftp://ftp.gnu.org's going-away party,
planned for November. Change these FTP URLs to https://ftp.gnu.org
instead. Make similar changes for URLs to other organizations moving
away from FTP. Also, change HTTP to HTTPS for URLs to gnu.org and
fsf.org when this works, as this will further help defend against
man-in-the-middle attacks (for this part I omitted the MS-DOS and
MS-Windows sources and the test tarballs to keep the workload down).
HTTPS is not fully working to lists.gnu.org so I left those URLs alone
for now.
