[tasklist] Done/PercentsComplete

Hi,

It is now possible to have a task that is done but it's percentsComplete
returns 0.

Here is how I want to change it:
1. done() means percentsComplete() == 100
2. if a task hasn't children it's percentComplete value is used
3. if a task has children then it's percentsComplete() returns average of
children's percentsComplete()

Suggestions/criticism are welcome.

Tim