Allow use of [T] in internal output messages for non-cycling tasks.

In principle you don't need to use [T] as a cycle time placeholder for
non-cycling tasks (for which T is 1) but if you do it should work.
Corrected a comment.
Merge pull request #379 from hjoliver/async-task-internal-outputs

Allow use of [T] in internal output messages for non-cycling tasks.