clarified export_files: Isabelle_System.copy_file_base preserves given directory sub-structure;
tuned concrete syntax;
syntax: glob
*~
*.class
*.jar
*.marks
*.orig
*.rej
.DS_Store
.swp
syntax: regexp
^contrib
^heaps/
^browser_info/
^doc/.*\.pdf
^src/Tools/jEdit/dist/
^src/Tools/VSCode/out/
^src/Tools/VSCode/extension/node_modules/
^Admin/jenkins/ci-extras/target/