Add a scrape command so I can work out if trackers are seeing my test clients

I don't even know if scrape is the right word.

cmd/scrape/main.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"bitbucket.org/anacrolix/go.torrent"
+	"bitbucket.org/anacrolix/go.torrent/tracker"
+	_ "bitbucket.org/anacrolix/go.torrent/tracker/udp"
+	"flag"
+	metainfo "github.com/nsf/libtorgo/torrent"
+	"log"
+	"os"
+)
+
+func main() {
+	flag.Parse()
+	mi, err := metainfo.Load(os.Stdin)
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, tier := range mi.AnnounceList {
+		for _, url := range tier {
+			tr, err := tracker.New(url)
+			if err != nil {
+				log.Fatal(err)
+			}
+			err = tr.Connect()
+			if err != nil {
+				log.Fatal(err)
+			}
+			resp, err := tr.Announce(&tracker.AnnounceRequest{
+				NumWant:  -1,
+				InfoHash: torrent.BytesInfoHash(mi.InfoHash),
+			})
+			if err != nil {
+				log.Fatal(err)
+			}
+			log.Print(resp)
+		}
+	}
+}