Prefetch support

Closes #3 (closed).

client.cc

@@ -186,10 +186,6 @@ void Client::upload(int fd, const Digest& digest)
 	}
 }
 
-/*void Client::prefetch(const Digest& digest)
-{
-}*/
-
 bool Client::batch_download_add(const Digest& digest)
 {
 	assert(!this->batch_read_request_sent);