use "Metis_" prefix rather than "Metis" structure;
the prefix can then be used not only for structures but also signatures and functors. A few other changes were made to the script, to eliminate the need for "metis_env.ML".
#!/usr/bin/env bash
#
# Author: Makarius
#
# DESCRIPTION: Update standard keyword files for Emacs Proof General
ISABELLE_HOME="$(isabelle getenv -b ISABELLE_HOME)"
LOG="$(isabelle getenv -b ISABELLE_OUTPUT)"/log
cd "$ISABELLE_HOME/etc"
isabelle keywords \
"$LOG/Pure.gz" "$LOG/HOL.gz" "$LOG/HOLCF.gz" "$LOG/HOL-Boogie.gz" \
"$LOG/HOL-Nominal.gz" "$LOG/HOL-Statespace.gz"
isabelle keywords -k ZF \
"$LOG/Pure.gz" "$LOG/FOL.gz" "$LOG/ZF.gz"