noweb-start and noweb-end header args

[Amy Grinn]

I would like to add support for setting 'org-babel-noweb-wrap-start and
'org-babel-noweb-wrap-end for each src block individually using the
header args :noweb-start and :noweb-end:

#+name: firewall-safe-mode
#+begin_src sh
  echo "Firewall is now in safe mode."
#+end_src

#+name: firewall
#+begin_src sh  :noweb yes :noweb-start <<< :noweb-end >>>
  safe_mode () {
      echo "Error encountered, switching to safe mode."
      <<<firewall-safe-mode>>>
      exit 1
  }

  setup-firewall || safe_mode
#+end_src

#+begin_src sh :noweb yes :noweb-start ":-) " :noweb-end " (-:" :tangle 
"test.sh"
  # Setup firewall
  :-) firewall (-:

  # Do other things
#+end_src


Here is a simple way to implement this feature.

diff --git a/lisp/ob-core.el b/lisp/ob-core.el
index 4dcfbd3b0..0be19ff06 100644
--- a/lisp/ob-core.el
+++ b/lisp/ob-core.el
@@ -194,15 +194,17 @@ This string must include a \"%s\" which will be replaced 
by the results."
   :package-version '(Org . "9.1")
   :safe #'booleanp)
 
-(defun org-babel-noweb-wrap (&optional regexp)
+(defun org-babel-noweb-wrap (&optional regexp info)
   "Return regexp matching a Noweb reference.
 
 Match any reference, or only those matching REGEXP, if non-nil.
 
 When matching, reference is stored in match group 1."
-  (concat (regexp-quote org-babel-noweb-wrap-start)
+  (concat (regexp-quote (or (cdr (assq :noweb-start (nth 2 info)))
+                            org-babel-noweb-wrap-start))
          (or regexp "\\([^ \t\n]\\(?:.*?[^ \t\n]\\)?\\)")
-         (regexp-quote org-babel-noweb-wrap-end)))
+         (regexp-quote (or (cdr (assq :noweb-end (nth 2 info)))
+                            org-babel-noweb-wrap-end))))
 
 (defvar org-babel-src-name-regexp
   "^[ \t]*#\\+name:[ \t]*"
@@ -3116,7 +3118,7 @@ block but are passed literally to the \"example-block\"."
                                   (not (equal (cdr v) "no"))))))
         (noweb-re (format "\\(.*?\\)\\(%s\\)"
                           (with-current-buffer parent-buffer
-                            (org-babel-noweb-wrap)))))
+                            (org-babel-noweb-wrap nil info)))))
     (unless (equal (cons parent-buffer
                          (with-current-buffer parent-buffer
                            (buffer-chars-modified-tick)))