src/Tools/Metis/fix_metis_license

clarified NEWS: document_files are officially required since Isabelle2014, but the absence was tolerated as legacy feature;

#!/usr/bin/env bash
THIS=$(cd "$(dirname "$0")"; echo $PWD)
(cd $THIS;
 perl -p -i~ -w -e 's/MIT license/BSD License/g' Makefile src/*.s* scripts/mlpp)