increased treshold for "this expression could be extremely ambigous" warning

--- a/src/Pure/Syntax/parser.ML	Tue Mar 12 19:20:23 2002 +0100
+++ b/src/Pure/Syntax/parser.ML	Thu Mar 14 16:00:29 2002 +0100
@@ -693,7 +693,7 @@
 
 
 val warned = ref false;                            (*flag for warning message*)
-val branching_level = ref 400;                   (*trigger value for warnings*)
+val branching_level = ref 600;                   (*trigger value for warnings*)
 
 (*get all productions of a NT and NTs chained to it which can
   be started by specified token*)