clean up two macros in ob-comint

* lisp/ob-comint.el (org-babel-comint-with-output,
org-babel-comint-in-buffer): clean up code.

This patch replaces some deeply nested ca/dr calls with ‘nth’, and
replaces a setq/unwind-protect/setq incantation with a simple let
binding.  Finally, it also restructures ’org-babel-comint-in-buffer’
to not needlessly save/restore match and excursion data if the buffer
process is not live, and to use with-current-buffer instead of
save-excursion+set-buffer
(info "(elisp) Excursions")

lisp/ob-comint.el

@@ -48,12 +48,12 @@ BUFFER is checked with `org-babel-comint-buffer-livep'.  BODY is
 executed inside the protection of `save-excursion' and
 `save-match-data'."
   (declare (indent 1))
-  `(save-excursion
+  `(progn
+     (unless (org-babel-comint-buffer-livep ,buffer)
+       (error "Buffer %s does not exist or has no process" ,buffer))
      (save-match-data
-       (unless (org-babel-comint-buffer-livep ,buffer)
-         (error "Buffer %s does not exist or has no process" ,buffer))
-       (set-buffer ,buffer)
-       ,@body)))
+       (with-current-buffer ,buffer
+	 ,@body))))
 (def-edebug-spec org-babel-comint-in-buffer (form body))
 
 (defmacro org-babel-comint-with-output (meta &rest body)
@@ -69,46 +69,42 @@ elements are optional.
 This macro ensures that the filter is removed in case of an error
 or user `keyboard-quit' during execution of body."
   (declare (indent 1))
-  (let ((buffer (car meta))
-	(eoe-indicator (cadr meta))
-	(remove-echo (cadr (cdr meta)))
-	(full-body (cadr (cdr (cdr meta)))))
+  (let ((buffer (nth 0 meta))
+	(eoe-indicator (nth 1 meta))
+	(remove-echo (nth 2 meta))
+	(full-body (nth 3 meta)))
     `(org-babel-comint-in-buffer ,buffer
-       (let ((string-buffer "") dangling-text raw)
-	 ;; setup filter
-	 (setq comint-output-filter-functions
-	       (cons (lambda (text) (setq string-buffer (concat string-buffer text)))
-		     comint-output-filter-functions))
-	 (unwind-protect
-	     (progn
-	       ;; got located, and save dangling text
-	       (goto-char (process-mark (get-buffer-process (current-buffer))))
-	       (let ((start (point))
-		     (end (point-max)))
-		 (setq dangling-text (buffer-substring start end))
-		 (delete-region start end))
-	       ;; pass FULL-BODY to process
-	       ,@body
-	       ;; wait for end-of-evaluation indicator
-	       (while (progn
-			(goto-char comint-last-input-end)
-			(not (save-excursion
-			       (and (re-search-forward
-				     (regexp-quote ,eoe-indicator) nil t)
-				    (re-search-forward
-				     comint-prompt-regexp nil t)))))
-		 (accept-process-output (get-buffer-process (current-buffer)))
-		 ;; thought the following this would allow async
-		 ;; background running, but I was wrong...
-		 ;; (run-with-timer .5 .5 'accept-process-output
-		 ;; 		 (get-buffer-process (current-buffer)))
-		 )
-	       ;; replace cut dangling text
-	       (goto-char (process-mark (get-buffer-process (current-buffer))))
-	       (insert dangling-text))
-	   ;; remove filter
-	   (setq comint-output-filter-functions
-		 (cdr comint-output-filter-functions)))
+       (let ((string-buffer "")
+	     (comint-output-filter-functions
+	      (cons (lambda (text) (setq string-buffer (concat string-buffer text)))
+		    comint-output-filter-functions))
+	     dangling-text raw)
+	 ;; got located, and save dangling text
+	 (goto-char (process-mark (get-buffer-process (current-buffer))))
+	 (let ((start (point))
+	       (end (point-max)))
+	   (setq dangling-text (buffer-substring start end))
+	   (delete-region start end))
+	 ;; pass FULL-BODY to process
+	 ,@body
+	 ;; wait for end-of-evaluation indicator
+	 (while (progn
+		  (goto-char comint-last-input-end)
+		  (not (save-excursion
+			 (and (re-search-forward
+			       (regexp-quote ,eoe-indicator) nil t)
+			      (re-search-forward
+			       comint-prompt-regexp nil t)))))
+	   (accept-process-output (get-buffer-process (current-buffer)))
+	   ;; thought the following this would allow async
+	   ;; background running, but I was wrong...
+	   ;; (run-with-timer .5 .5 'accept-process-output
+	   ;; 		 (get-buffer-process (current-buffer)))
+	   )
+	 ;; replace cut dangling text
+	 (goto-char (process-mark (get-buffer-process (current-buffer))))
+	 (insert dangling-text)
+
 	 ;; remove echo'd FULL-BODY from input
 	 (if (and ,remove-echo ,full-body
 		  (string-match