org-babel: allow multiple spaces/tabs between "src" and lang

contrib/babel/lisp/org-babel.el

@@ -109,7 +109,7 @@ then run `org-babel-pop-to-session'."
 (defun org-babel-set-interpreters (var value)
   (set-default var value)
   (setq org-babel-src-block-regexp
-	(concat "^[ \t]*#\\+begin_src \\("
+	(concat "^[ \t]*#\\+begin_src[ \t]+\\("
 		(mapconcat 'regexp-quote value "\\|")
 		"\\)[ \t]*"
                 "\\([ \t]+\\([^\n]+\\)\\)?\n" ;; match header arguments