add leveldb support for needle map

This supposedly should reduce memory consumption. However, for tests
with millions of, this shows consuming more memories. Need to see
whether this will work out. If not, later boltdb will be tested.

go/weed/compact.go

@@ -33,7 +33,7 @@ func runCompact(cmd *Command, args []string) bool {
 	}
 
 	vid := storage.VolumeId(*compactVolumeId)
-	v, err := storage.NewVolume(*compactVolumePath, *compactVolumeCollection, vid, nil, nil)
+	v, err := storage.NewVolume(*compactVolumePath, *compactVolumeCollection, vid, false, nil, nil)
 	if err != nil {
 		glog.Fatalf("Load Volume [ERROR] %s\n", err)
 	}