I've convinced myself that nothing in DaemonStatus can deadlock,
as it always keepts the TMVar full. That was the only reason it was in the
Annex monad.
This should fix OSX/BSD issues with not noticing transfer information
files with kqueue. Now that threads are used, the thread can manage the
transfer slot allocation and deallocation by itself; much cleaner.
There's still a bug; if the child updates its transfer info file,
then the data from it will superscede the TransferInfo, losing the
info that we should wait on this child.
