Task_Queue.update_timing: more precise treatment of interruptibility; Task_Queue.waiting: potentially expensive wait dependencies are subject to trace flag;

Lazy.force_result: more standard treatment of interruptibility, potentially addressing races of exceptions vs. interrupts;

thm_proof: visible fulfill_body only, without joining nested thms -- retain proof irrelevance, which is important for parallel performance;

tuned comments;

clarified Proofterm.proofs_enabled;

explicit is better than implicit;

tuned odd conditional expression;

eliminated slightly odd abstract type Task_Queue.deps; tuned signature; tuned;

merged

Introduction of metis calls and other cosmetic modifications.