add keywords of this node as well (e.g. relevant for Pure.thy);

--- a/src/Pure/Thy/thy_load.scala	Wed Aug 22 21:28:33 2012 +0200
+++ b/src/Pure/Thy/thy_load.scala	Wed Aug 22 21:43:17 2012 +0200
@@ -108,7 +108,7 @@
       {
         val string = text.toString
         val header = check_thy_text(name, string)
-        val more_uses = find_files(syntax, string)
+        val more_uses = find_files(syntax.add_keywords(header.keywords), string)
         header.copy(uses = header.uses ::: more_uses.map((_, false)))
       })
 }