This is now self-maintaining and doesn't rely on the async pool to wipe its ass on task completion. Instead, the garbage collector will cause thread-local data to be automatically released when the async task is garbage-collected on the main thread.
This brings two plugin-breaking changes: AsyncTask->onCompletion() and AsyncTask->onProgressUpdate() no longer accept Server parameters.
This now allows for the functionality of AsyncPool and AsyncTask to be tested outside of a Server.
I am eating my own words this once, because having the tester plugin as a separate repository makes no sense - it is just added barriers to writing proper tests with no actual benefit. Since the tester plugin is specifically intended for CI, it doesn't make sense for it to be in its own module.
