Drop peers for sending too many unwanted pieces

So the algorithm is now, drop the worst half if they get too old, and drop any connection if it's ratio is poor.

torrent.go

@@ -745,14 +745,17 @@ func (t *torrent) extentPieces(off, _len int64) (pieces []int) {
 func (t *torrent) worstBadConn(cl *Client) *connection {
 	wcs := t.worstConns(cl)
 	heap.Init(wcs)
-	// A connection can only be bad if it's in the worst half, rounded down.
-	for wcs.Len() > (socketsPerTorrent+1)/2 {
+	for wcs.Len() != 0 {
 		c := heap.Pop(wcs).(*connection)
-		// Give connections 1 minute to prove themselves.
-		if time.Since(c.completedHandshake) < time.Minute {
-			continue
+		if c.UnwantedChunksReceived >= 6 && c.UnwantedChunksReceived > c.UsefulChunksReceived {
+			return c
+		}
+		if wcs.Len() >= (socketsPerTorrent+1)/2 {
+			// Give connections 1 minute to prove themselves.
+			if time.Since(c.completedHandshake) > time.Minute {
+				return c
+			}
 		}
-		return c
 	}
 	return nil
 }