merged

updated properties for scala.concurrent.ExecutionContext.Implicits.global (future task farm), similar to Isabelle/ML; removed obsolete properties for old actors;

simplified change_buffer (again, see 937826d702d5): no thread, just timer, rely on asynchronous commands_changed.post;

replaced manager Actor by Consumer_Thread, which is lazy to defer its start to actual Handler init time;

tuned whitespace;

obsolete;

clarified Session.Consumer, with Session.Outlet managed by dispatcher thread; eliminated old actors;

tuned comments;

more robust prover termination;

more explicit checks;

tuned signature;

more uniform warning/error handling, potentially with propagation to send_wait caller;

more careful shutdown (amending f2f53f7046f4);

misc tuning;

obsolete;

converted main session manager to Consumer_Thread: messages need to be consumed immediately, postponed_changes replaces implicit actor mailbox scanning;

simplified commands_changed_buffer (in contrast to a8331fb5c959): rely on better performance of Consumer_Thread/Mailbox and more direct Timer (like session_actor.receiver);

simplified -- prefer Consumer_Thread over Actor;

tuned imports;

support for requests with explicit acknowledgment (and exception propagation);

more robust thread: continue after failure;

clarified command_input: Consumer_Thread;

further robustification wrt. unclear ranges;

allow more control of main loop; more robust is_active test, although thread could terminate at any time;

eliminated pointless output actors; clarified command_input, which already includes thread.join;

more robust shutdown; less ooddities;

consumer thread with unbounded queueing of requests (similar to Message_Channel in ML);

proper signaling after each state update (NB: ML version does this uniformly via timed_access);

added Mailbox, as in ML;

synchronized access, similar to ML version;