- now tracks downloads globally too, so it doesn't request the same
object from multiple peers at the same time
- retries at the earliest every minute
- stops trying to download an object after an hour
- minor fixes in retrying downloading invalid objects
- should prevent the same object being re-requested indefinitely
- locking for object tracking
- move SSL-specific error handling to TLSDispatcher
- observe maximum connection limit when accepting a new connection
- stack depth test (for debugging purposes)
- separate download thread
- connection pool init moved to main thread