clarified Isabelle/ML bootstrap, such that Execution does not require ML_Compiler;
#!/usr/bin/env bash
#
# Author: Makarius
#
# DESCRIPTION: invoke Scala compiler within the Isabelle environment
isabelle_admin_build jars || exit $?
isabelle_scala scalac -Dfile.encoding=UTF-8 \
-classpath "$(jvmpath "$ISABELLE_CLASSPATH")" "$@"