org-babel-execute-src-block: Force :dir according to live session

* lisp/ob-core.el (org-babel-execute-src-block): Force eval directory
to follow live session buffer, if any.  This is consistent with what
we promise in the manual section "16.4 Environment of a Code
Block">Choosing a working directory.

Link: https://orgmode.org/list/87mssi8ht2.fsf@gmail.com

lisp/ob-core.el

@@ -842,6 +842,9 @@ guess will be made."
 		 (default-directory
 		  (cond
 		   ((not dir) default-directory)
+                   ((when-let ((session (cdr (assq :session params))))
+                      (when (org-babel-comint-buffer-livep session)
+                        (buffer-local-value 'default-directory (get-buffer session)))))
 		   ((member mkdirp '("no" "nil" nil))
 		    (file-name-as-directory (expand-file-name dir)))
 		   (t