more accurate classpath for "isabelle scala";

--- a/lib/Tools/scala	Sun May 24 19:45:42 2020 +0200
+++ b/lib/Tools/scala	Sun May 24 20:35:24 2020 +0200
@@ -13,5 +13,9 @@
   SCALA_ARGS["${#SCALA_ARGS[@]}"]="-J$ARG"
 done
 
+[ -n "$CLASSPATH" ] && classpath "$CLASSPATH"
+unset CLASSPATH
+
 isabelle_scala scala "${SCALA_ARGS[@]}" \
-  -classpath "$(platform_path "$ISABELLE_CLASSPATH")" "$@"
+  -classpath "$(platform_path "$ISABELLE_CLASSPATH")" \
+  -Disabelle.scala.classpath="$(platform_path "$ISABELLE_CLASSPATH")" "$@"

--- a/src/Pure/System/scala.scala	Sun May 24 19:45:42 2020 +0200
+++ b/src/Pure/System/scala.scala	Sun May 24 20:35:24 2020 +0200
@@ -31,7 +31,7 @@
 
       val class_path =
         for {
-          prop <- List("scala.boot.class.path", "java.class.path")
+          prop <- List("isabelle.scala.classpath", "java.class.path")
           path = System.getProperty(prop, "") if path != "\"\""
           elem <- space_explode(JFile.pathSeparatorChar, path)
         } yield elem