use Content-Digest header in HEAD requests instead of length (to track non-monotone changes);

merged

Simplification of sin, cos, exp of multiples of pi

minor performance tuning: more compact data;

removed unused/inefficient size_of_proof (see also 2241191a3c54);

tuned;

more robust: avoid crash of sleep() for negative time;

clarified signature;

clarified signature: more explicit types;

support "rsync --chmod --chown" via Rsync.Context;

tuned;

bash: proper bash_process via SSH; getenv: prefer light-weight ssh.execute;

clarified signature: support explicit cwd;

support bash via SSH;

clarified comments;

proper support for remote cwd;

clarified context for (remote) bash scripts: export variables are optional, support cwd;

more operations for SSH.System: bash_process and bash;

unused;

clarified signature: prefer symbolic isabelle.Path over physical java.io.File;

minor performance tuning;

merged

minor performance tuning: save approx. 70ms per SSH command;

minor performance tuning: save approx. 70ms per SSH command;

minor performance tuning: save approx. 70ms per SSH test command;

suport Isabelle_System.bash via SSH.System;

more operations;

tuned;

clarified signature;

clarified signature;