edit-prep: language specific src-edit buffer preparation, with R session association

* lisp/ob-R.el (org-babel-edit-prep:R): Associate the appropriate R
  process with the edit buffer when :session is specified.

* lisp/org-src.el (org-edit-src-code): Allow language-specific
  edit-buffer preparation by calling the org-babel-edit-prep:lang
  function when it is defined.

lisp/ob-R.el

@@ -51,6 +51,12 @@
 (defvar org-babel-R-command "R --slave --no-save"
   "Name of command to use for executing R code.")
 
+(defun org-babel-edit-prep:R (info)
+  (let ((session (cdr (assoc :session (nth 2 info)))))
+    (when (and session (string-match "^\\*\\(.+?\\)\\*$" session))
+      (save-match-data (org-babel-R-initiate-session session nil))
+      (setq ess-local-process-name (match-string 1 session)))))
+
 (defun org-babel-expand-body:R (body params &optional graphics-file)
   "Expand BODY according to PARAMS, return the expanded body."
   (let ((graphics-file

lisp/org-src.el

@@ -214,6 +214,7 @@ buffer."
   (let ((mark (and (org-region-active-p) (mark)))
 	(case-fold-search t)
 	(info (org-edit-src-find-region-and-lang))
+	(full-info (org-babel-get-src-block-info))
 	(org-mode-p (or (org-mode-p) (derived-mode-p 'org-mode)))
 	(beg (make-marker))
 	(end (make-marker))
@@ -323,7 +324,10 @@ buffer."
 	(org-src-mode)
 	(set-buffer-modified-p nil)
 	(and org-edit-src-persistent-message
-	     (org-set-local 'header-line-format msg)))
+	     (org-set-local 'header-line-format msg))
+	(let ((edit-prep-func (intern (concat "org-babel-edit-prep:" lang))))
+	  (when (fboundp edit-prep-func)
+	    (funcall edit-prep-func full-info))))
       t)))
 
 (defun org-edit-src-continue (e)