begin_theory: priority message to gain some robustness in sync communication;

--- a/src/Pure/Thy/thy_info.ML	Wed Sep 13 22:31:19 2000 +0200
+++ b/src/Pure/Thy/thy_info.ML	Wed Sep 13 22:32:15 2000 +0200
@@ -385,6 +385,7 @@
   let
     val assert_thy = if upd then quiet_update_thy true else weak_use_thy;
     val _ = check_unfinished error name;
+    val _ = priority (loader_msg "looking up" [name]);
     val _ = (map Path.basic parents; seq assert_thy parents);
     val theory = PureThy.begin_theory name (map get_theory parents);
     val deps =