ob-exp: on export resolve hashes in the current (not original) file buffer

* lisp/ob-exp.el (org-babel-exp-results): Resolve hashes in the
  current (not original) file buffer.
* lisp/ob.el (org-babel-current-result-hash): More informative name,
  and remove useless optional argument.

lisp/ob-exp.el

@@ -243,9 +243,7 @@ This function is called by `org-babel-exp-do-export'.  The code
 block will be evaluated.  Optional argument SILENT can be used to
 inhibit insertion of results into the buffer."
   (when (and org-export-babel-evaluate
-	     (not (and hash
-		       (equal hash (org-babel-exp-in-export-file (nth 0 info)
-				     (org-babel-result-hash info))))))
+	     (not (and hash (equal hash (org-babel-current-result-hash)))))
     (let ((lang (nth 0 info))
 	  (body (nth 1 info)))
       ;; skip code blocks which we can't evaluate

lisp/ob.el

@@ -782,9 +782,9 @@ the current subtree."
 			 (nth 1 info))))
 	 (sha1 it))))))
 
-(defun org-babel-result-hash (&optional info)
+(defun org-babel-current-result-hash ()
   "Return the in-buffer hash associated with INFO."
-  (org-babel-where-is-src-block-result nil info)
+  (org-babel-where-is-src-block-result)
   (org-babel-clean-text-properties (match-string 3)))
 
 (defun org-babel-hide-hash ()