PinnedDispatcher - uses single thread for all actors instead of creating persanal thread for every actor

[kantora]

In version 0.8.x it created personal thread for every actor. But now it uses single thread for all actors under same dispatcher (so, if you put PinnedDispatcher as default dispatcher - all actors in system will work in single thread without any multythreading).

Also I've found unused variable "running" in it. So, I suppose that thread will last forever, even after actor's death.

[rogeralsing]

cc @Aaronontheweb, the new dispatcherconfig stuff seems to have broken this

From Java docs:

PinnedDispatcher

This dispatcher dedicates a unique thread for each actor using it; i.e. each actor will have its own thread pool with only one thread in the pool.

• Sharability: None
• Mailboxes: Any, creates one per Actor
• Use cases: Bulkheading
• Driven by: Any akka.dispatch.ThreadPoolExecutorConfigurator
  by default a "thread-pool-executor

[Aaronontheweb]

Yep, this is a case of me misunderstanding the details of how the pinned dispatcher works. I'll fix this and add some garbage collection to it also.