added calculation.ML;

--- a/src/Pure/Isar/ROOT.ML	Fri Jun 04 19:53:03 1999 +0200
+++ b/src/Pure/Isar/ROOT.ML	Fri Jun 04 19:53:27 1999 +0200
@@ -13,6 +13,7 @@
 use "args.ML";
 use "attrib.ML";
 use "method.ML";
+use "calculation.ML";
 
 (*outer syntax*)
 use "comment.ML";