Add t/35-then-cancel.t
Add t/27-try.t
Fix bug in t/35-then-cancel.t. Misuse of is().
t/27-try.t: add tests for @args param.
Q.pm: implement all methods. fails t/30-then.t
Q.pm: re-implement then() with on_ready(). followed_by() method does not propagate cancellation downwards ($f1->cancel => $fseq->cancel). It supports upward-cancellation only ($fseq->cancel => $f1->cancel).
Add cyclic reference tests to t/30-then.t, t/35-then-cancel.t. Pass the tests.
Change test spec of t/41-error-dependent.t: then() method makes the dependent future "failure handled" state, and it propagates only the failure of the dependent future, not those of subfutures.