#3 TaskFuture needs to indicate whether task provides @Progress

[Malcolm]

A task with no @Progress method causes TaskFuture.progress() to return a generated instance with 0.0 or 1.0 depending on whether it's completed successfully or not.
So for a user of TaskFuture, there is no way to tell whether the task impl. has a @Progress method.
Sometimes this is useful, such as when computing overall application progress with some tasks that have progress and others that don't provide it.

[Malcolm]

Implemented (rev 33).
Needs some unit tests created for it.