Pacify some docstring control char warnings

Other instances are discussed in the following thread:
https://lists.gnu.org/r/emacs-devel/2024-02/msg00797.html

* lisp/allout.el (allout-command-prefix): Declare :type as
key-sequence.  Mark up key sequences in docstring.
* lisp/auth-source.el (auth-source--decode-octal-string):
* lisp/ffap.el (ffap-search-backward-file-end):
* lisp/gnus/gnus-art.el (gnus-page-delimiter):
* lisp/gnus/nnheader.el (nnheader-strip-cr):
* lisp/proced.el (proced-log):
* lisp/progmodes/idlw-shell.el (idlwave-shell-prompt-pattern):
* lisp/url/url-http.el (url-http-clean-headers):
* lisp/vcursor.el (vcursor-interpret-input): Quote control
characters in docstrings.

lisp/allout.el

@@ -161,9 +161,9 @@ respective `allout-mode' keybinding variables, `allout-command-prefix',
 (defcustom allout-command-prefix "\C-c "
   "Key sequence to be used as prefix for outline mode command key bindings.
 
-Default is `\C-c<space>'; just `\C-c' is more short-and-sweet, if you're
-willing to let allout use a bunch of \C-c keybindings."
-  :type 'string
+Default is \\`C-c SPC'; just \\`C-c' is more short-and-sweet, if you're
+willing to let allout use a bunch of \\`C-c' keybindings."
+  :type 'key-sequence
   :group 'allout-keybindings
   :set #'allout-compose-and-institute-keymap)
 ;;;_   = allout-keybindings-binding

lisp/auth-source.el

@@ -1985,7 +1985,7 @@ entries for git.gnus.org:
 
 
 (defun auth-source--decode-octal-string (string)
-  "Convert octal STRING to utf-8 string.  E.g: \"a\134b\" to \"a\b\"."
+  "Convert octal STRING to utf-8 string.  E.g.: \"a\\134b\" to \"a\\b\"."
   (let ((list (string-to-list string))
         (size (length string)))
     (decode-coding-string

lisp/ffap.el

@@ -1098,12 +1098,12 @@ Suppose the cursor is somewhere that might be near end of file,
 the guessing would position point before punctuation (like comma)
 after the file extension:
 
-  C:\temp\file.log, which contain ....
+  C:\\temp\\file.log, which contain ....
   =============================== (before)
   ---------------- (after)
 
 
-  C:\temp\file.log on Windows or /tmp/file.log on Unix
+  C:\\temp\\file.log on Windows or /tmp/file.log on Unix
   =============================== (before)
   ---------------- (after)
 

lisp/gnus/gnus-art.el

@@ -694,7 +694,7 @@ used as possible file names."
 
 (defcustom gnus-page-delimiter "^\^L"
   "Regexp describing what to use as article page delimiters.
-The default value is \"^\^L\", which is a form linefeed at the
+The default value is \"^\\^L\", which is a form linefeed at the
 beginning of a line."
   :type 'regexp
   :group 'gnus-article-various)

lisp/gnus/nnheader.el

@@ -1016,7 +1016,7 @@ See `find-file-noselect' for the arguments."
   (nnheader-skeleton-replace from to t))
 
 (defun nnheader-strip-cr ()
-  "Strip all \r's from the current buffer."
+  "Strip all \\r's from the current buffer."
   (nnheader-skeleton-replace "\r"))
 
 (define-obsolete-function-alias 'nnheader-cancel-timer 'cancel-timer "27.1")

lisp/proced.el

@@ -2261,7 +2261,7 @@ If LOG is a string and there are more args, it is formatted with
 those ARGS.  Usually the LOG string ends with a \\n.
 End each bunch of errors with (proced-log t signal):
 this inserts the current time, buffer and signal at the start of the page,
-and \f (formfeed) at the end."
+and \\f (formfeed) at the end."
   (let ((obuf (current-buffer)))
     (with-current-buffer (get-buffer-create proced-log-buffer)
       (goto-char (point-max))

lisp/progmodes/idlw-shell.el

@@ -96,8 +96,8 @@
 
 (defcustom idlwave-shell-prompt-pattern "^\r? ?IDL> "
   "Regexp to match IDL prompt at beginning of a line.
-For example, \"^\r?IDL> \" or \"^\r?WAVE> \".
-The \"^\r?\" is needed, to indicate the beginning of the line, with
+For example, \"^\\r?IDL> \" or \"^\\r?WAVE> \".
+The \"^\\r?\" is needed, to indicate the beginning of the line, with
 optional return character (which IDL seems to output randomly).
 This variable is used to initialize `comint-prompt-regexp' in the
 process buffer."

lisp/url/url-http.el

@@ -427,7 +427,7 @@ Use `url-http-referer' as the Referer-header (subject to `url-privacy-level')."
 
 ;; Parsing routines
 (defun url-http-clean-headers ()
-  "Remove trailing \r from header lines.
+  "Remove trailing \\r from header lines.
 This allows us to use `mail-fetch-field', etc.
 Return the number of characters removed."
   (let ((end (marker-position url-http-end-of-headers)))

lisp/vcursor.el

@@ -433,7 +433,7 @@ Default is nil."
 (defcustom vcursor-interpret-input nil
   "If non-nil, input from the vcursor is treated as interactive input.
 This will cause text insertion to be much slower.  Note that no special
-interpretation of strings is done: \"\C-x\" is a string of four
+interpretation of strings is done: \"\\C-x\" is a string of four
 characters.  The default is simply to copy strings."
   :type 'boolean
   :version "20.3")