datetree: Recognize year headline with tags as a match

* lisp/org-datetree.el (org-datetree-find-year-create): Also match
headlines with tags.

Change made to fix the problem where a year headline of a
datetree was not matched if it had a tag.  The :NOEXPORT: tag
is one useful case that should be matched.

Initial problem observation reported by Jeffrey McBeth on the
org-mode mailing list.

TINYCHANGE

lisp/org-datetree.el

@@ -72,7 +72,7 @@ tree can be found."
       (goto-char (prog1 (point) (widen))))))
 
 (defun org-datetree-find-year-create (year)
-  (let ((re "^\\*+[ \t]+\\([12][0-9][0-9][0-9]\\)\\s-*$")
+  (let ((re "^\\*+[ \t]+\\([12][0-9]\\{3\\}\\)\\(.*?\\([ \t]:[[:alnum:]:_@#%]+:\\)?\\s-*$\\)")
 	match)
     (goto-char (point-min))
     (while (and (setq match (re-search-forward re nil t))