added THIS_IS_ISABELLE_BUILD discrimination;

--- a/etc/settings	Mon Mar 10 10:32:32 1997 +0100
+++ b/etc/settings	Tue Mar 11 13:05:11 1997 +0100
@@ -56,7 +56,13 @@
 # Heap file in/out locations.
 # Note: ML system and platform info is appended automatically!
 ISABELLE_PATH=$ISABELLE_HOME_USER/heaps:$ISABELLE_HOME/heaps
-ISABELLE_OUTPUT=$ISABELLE_HOME_USER/heaps
+
+if [ "$THIS_IS_ISABELLE_BUILD" = true ]; then
+  ISABELLE_OUTPUT=$ISABELLE_HOME/heaps
+else
+  ISABELLE_OUTPUT=$ISABELLE_HOME_USER/heaps
+fi
+
 
 DEFAULT_LOGIC=HOL