Summary
- merged
- tuyned
- further robustification (amending 772bdd1ed843);
- added function
- merged
- new material on topology: products, etc. Some renamings, esp continuous_on_topo -> continuous_map
- proper ISABELLE_OCAML_VERSION;
- less ambitious test: lapbroy68 lacks libgmp-dev that is required for ocaml setup of zarith;
- more robust "switch create"; disable sandboxing to avoid dependency on bubblewrap (unavailable on Ubuntu 16.04);
- prefer central root: just one copy of this bulky material;
- updated to current opam-2.0.3, which is also the version provided by Cygwin 3.0.4;