added remote_build_history tasks: parallel on several remote hosts; isabelle_identify: use self repos for robustness; more logger context: options and ssh; setup repository clones on demand; clarified target repositories;

added setup_repository; clarified root: expanded in target environment;

more operations;

expand relatively to given environment, notably remote HOME;

tuned;

tuned signature;

tuned;

clarified treatment of non-text bytes;

remove invocation of build_history: results are reported via stdout;

clarified signature;