org-publish: Fix regexp for include files

* org-publish.el (org-publish-cache-file-needs-publishing): Regexp did
  not find includes with double quoted file names.

TINYCHANGE

lisp/org-publish.el

@@ -1108,7 +1108,7 @@ so that the file including them will be republished as well."
       (when (equal (file-name-extension filename) "org")
 	(find-file (expand-file-name filename))
 	(goto-char (point-min))
-	(while (re-search-forward "^#\\+INCLUDE: \\(.+\\)[ ^\t]*$" nil t)
+	(while (re-search-forward "^#\\+INCLUDE:[ \t]+\"?\\([^ \t\"]*\\)\"?[ \t]*.*$" nil t)
 	  (let* ((included-file (expand-file-name (match-string 1))))
 	    (add-to-list 'included-files-ctime
 			 (org-publish-cache-ctime-of-src included-file) t)))))