The checking code has bad run time characteristics and would need to be fixed
for large projects with deep task dependency chains.
The code in sbt.Execute has been in production for a long time so it seems safe
enough to drop the extra checks by default. To debug issues, you can set
`-Dsbt.execute.extrachecks=true` to revert to the old behavior.
Set sbt.task.timings=true to print timings for tasks.
This sample progress handler shows how to get names for tasks and
deal with flatMapped tasks. There are still some tasks that make
it through as anonymous, which needs to be investigated.
A setting to provide a custom handler should come in a subsequent commit.