directory structure change to work with glide

glide has its own requirements. My previous workaround caused me some
code checkin errors. Need to fix this.

weed/topology/topology_event_handling.go

@@ -0,0 +1,74 @@
+package topology
+
+import (
+	"math/rand"
+	"time"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/storage"
+)
+
+func (t *Topology) StartRefreshWritableVolumes(garbageThreshold string) {
+	go func() {
+		for {
+			if t.IsLeader() {
+				freshThreshHold := time.Now().Unix() - 3*t.pulse //3 times of sleep interval
+				t.CollectDeadNodeAndFullVolumes(freshThreshHold, t.volumeSizeLimit)
+			}
+			time.Sleep(time.Duration(float32(t.pulse*1e3)*(1+rand.Float32())) * time.Millisecond)
+		}
+	}()
+	go func(garbageThreshold string) {
+		c := time.Tick(15 * time.Minute)
+		for _ = range c {
+			if t.IsLeader() {
+				t.Vacuum(garbageThreshold)
+			}
+		}
+	}(garbageThreshold)
+	go func() {
+		for {
+			select {
+			case v := <-t.chanFullVolumes:
+				t.SetVolumeCapacityFull(v)
+			case dn := <-t.chanRecoveredDataNodes:
+				t.RegisterRecoveredDataNode(dn)
+				glog.V(0).Infoln("DataNode", dn, "is back alive!")
+			case dn := <-t.chanDeadDataNodes:
+				t.UnRegisterDataNode(dn)
+				glog.V(0).Infoln("DataNode", dn, "is dead!")
+			}
+		}
+	}()
+}
+func (t *Topology) SetVolumeCapacityFull(volumeInfo storage.VolumeInfo) bool {
+	vl := t.GetVolumeLayout(volumeInfo.Collection, volumeInfo.ReplicaPlacement, volumeInfo.Ttl)
+	if !vl.SetVolumeCapacityFull(volumeInfo.Id) {
+		return false
+	}
+	for _, dn := range vl.vid2location[volumeInfo.Id].list {
+		if !volumeInfo.ReadOnly {
+			dn.UpAdjustActiveVolumeCountDelta(-1)
+		}
+	}
+	return true
+}
+func (t *Topology) UnRegisterDataNode(dn *DataNode) {
+	for _, v := range dn.GetVolumes() {
+		glog.V(0).Infoln("Removing Volume", v.Id, "from the dead volume server", dn)
+		vl := t.GetVolumeLayout(v.Collection, v.ReplicaPlacement, v.Ttl)
+		vl.SetVolumeUnavailable(dn, v.Id)
+	}
+	dn.UpAdjustVolumeCountDelta(-dn.GetVolumeCount())
+	dn.UpAdjustActiveVolumeCountDelta(-dn.GetActiveVolumeCount())
+	dn.UpAdjustMaxVolumeCountDelta(-dn.GetMaxVolumeCount())
+	dn.Parent().UnlinkChildNode(dn.Id())
+}
+func (t *Topology) RegisterRecoveredDataNode(dn *DataNode) {
+	for _, v := range dn.GetVolumes() {
+		vl := t.GetVolumeLayout(v.Collection, v.ReplicaPlacement, v.Ttl)
+		if vl.isWritable(&v) {
+			vl.SetVolumeAvailable(dn, v.Id)
+		}
+	}
+}