work on CCall case

up to last part, showing that the generated bytecode for the call gets
stuck if the semantics says Timeout is raised.
more CCall case, but want to rework statement again

can maybe collapse the two exception cases into one... at the moment the
timeout exception case needs extra hypotheses saying what the stack
looks like in tail position...
finish CCall case (probably)

haven't re-checked the script, but the goal was proved interactively
(gotta go now)