Merge pull request #1068 from Agoric/894-fix-liveslots-and-tests

rewrite liveslots use of HandledPromise, remove deliver() stall

refs #894
refs #930 (should unblock, although rewrites will be needed)
refs #767 refs #766 (should unblock)
closes #1053 (includes rebased form of the PR)
closes #769 (incidentally)