Send orphan hash in notifications instead of root.

Rather than sending the root of the an orphan chain when sending an orphan
notification, send the hash of the orphan block itself.  The caller can
then call the GetOrphanRoot function with the hash to get the root of the
orphan chain as needed.  This is being changed since it's cleaner and more
detministic sending the hash for the orphan block that was just processed
rather than sending a possibly different hash depending on whether there
is an orphan chain or not.