etc/options

--- a/etc/options	Fri Mar 01 20:16:26 2019 +0100
+++ b/etc/options	Fri Mar 01 21:29:59 2019 +0100
@@ -116,6 +116,9 @@
 option profiling : string = ""
   -- "ML profiling (possible values: time, allocations)"
 
+option system_heaps : bool = false
+  -- "store session heaps in $ISABELLE_HEAPS_SYSTEM, not $ISABELLE_HEAPS"
+
 
 section "ML System"