Previously, some code executed in a timer, which could execute in the
wrong buffer, leading to a hang.

* lisp/eshell/esh-proc.el (eshell-sentinel): Use 'with-current-buffer'
in the timer function.

* test/lisp/eshell/esh-proc-tests.el (eshell-test-value): New variable.
(esh-proc-test/sentinel/change-buffer): New test.

The previous implementation in 6ae2b74ed20 only stopped at prompts,
which isn't the right behavior (bug#61545).

* lisp/eshell/em-prompt.el (eshell-forward-paragraph)
(eshell-backward-paragraph): Reimplement to handle prompts and
paragraphs (the latter by calling the original 'forward-paragraph').

* test/lisp/eshell/em-prompt-tests.el
(em-prompt-test/next-previous-prompt/multiline): Rename.
(em-prompt-test/forward-backward-paragraph-1): New function.
(em-prompt-test/forward-backward-paragraph)
(em-prompt-test/forward-backward-paragraph/multiline): New tests.

Both Comint and Eshell do this, and it can significantly slow down
commands that write a lot of output (bug#71576).

* lisp/comint.el (comint-password-prompt-max-length): New variable...
(comint-watch-for-password-prompt): ... use it.  Additionally, use the
matched result for the Emacs-based password prompt.

* lisp/eshell/esh-mode.el (eshell-password-prompt-max-length): New
variable...
(eshell-watch-for-password-prompt): ... use it.

* etc/NEWS: Announce this change.

* lisp/eshell/esh-arg.el (eshell-quote-argument): Mention that this
function is for use within Eshell buffers.
(eshell-quote-backslash): Properly quote newlines.

* lisp/eshell/em-unix.el (eshell/cat, eshell/du): Throw
'eshell-external' instead; that's what it's here for.

* test/lisp/eshell/esh-proc-tests.el (esh-proc-test-quote-argument):
Remove.
(esh-proc-test/emacs-command):
* test/lisp/eshell/esh-var-tests.el (esh-var-test/path-var/set)
(esh-var-test/path-var/set-locally): Use 'eshell-quote-argument'.

* test/lisp/eshell/em-unix-tests.el (em-unix-test/compile/interactive):
Use 'shell-quote-argument' (Note: *not* 'eshell-...').

* lisp/eshell/esh-proc.el (eshell-gather-process-output): Don't force
POSIX syntax.  This is less confusing when running on MS-Windows.

This improves the logic for copying/stealing handles when constructing
the command form: now, we should always steal the handles for the last
real command, even if there were some trailing semicolons.

* lisp/eshell/esh-arg.el (eshell-parse-delimiter): Be stricter about
parsing so that things like "& &" aren't parsed as a single "&&" token.

* lisp/eshell/esh-cmd.el (eshell-parse-command): Get the commands in
reverse, and remove any nil commands.
(eshell-split-commands): Always return the trailing terms (except when
there were no terms to begin with).

* test/lisp/eshell/esh-cmd-tests.el
(esh-cmd-test/empty-background-command): New test.

* lisp/eshell/em-script.el (eshell-close-target): New function.

* test/lisp/eshell/em-script-tests.el (em-script-test/batch-file): New
test; rename old one to...
(em-script-test/batch-file/shebang): ... this.

* lisp/eshell/esh-util.el (eshell-get-path): Don't add "." if it
is already there.

* test/lisp/eshell/esh-var-tests.el
(esh-var-test/path-var/preserve-across-hosts): Skip on MS-Windows.
(esh-var-test/path-var/set, esh-var-test/path-var/set-locally):
Quote the PATH value, for MS-Windows.
* test/lisp/eshell/esh-util-tests.el (esh-util-test/path/get): No
need to add ".": it is already done by 'eshell-get-path'.
* test/lisp/eshell/esh-proc-tests.el
(esh-proc-test/kill-pipeline): Accept empty string as valid
output.
(esh-proc-test/sigpipe-exits-process): Skip on MS-Windows: no
SIGPIPE.
(esh-proc-test/emacs-command): Quote correctly for MS-Windows.
* test/lisp/eshell/em-unix-tests.el
(em-unix-test/compile/interactive): Fix test on MS-Windows.
* test/lisp/eshell/em-script-tests.el (em-script-test/batch-file):
Skip on MS-Windows.
* test/lisp/eshell/eshell-tests-helpers.el
(eshell-command-result--equal): Compare strings (file names)
case-insensitively on MS-Windows.