notable performance tuning (amending a59d9b81be24 and 8976c5bc9e97): avoid costly could_beta_eta_contract, which traverses the whole term;
always use Item_Net.retrieve instead, but on frozen TVars/Vars to enforce matching instead of unification;
syntax: glob
*~
*.class
*.jar
*.marks
*.orig
*.rej
*.vsix
.DS_Store
.swp
syntax: regexp
^contrib
^heaps/
^browser_info/
^doc/.*\.pdf
^src/Tools/VSCode/extension/out/
^src/Tools/VSCode/extension/node_modules/
^Admin/jenkins/ci-extras/target/