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/operation/lookup_vid_cache.go

@@ -0,0 +1,51 @@
+package operation
+
+import (
+	"errors"
+	"strconv"
+	"time"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+type VidInfo struct {
+	Locations       []Location
+	NextRefreshTime time.Time
+}
+type VidCache struct {
+	cache []VidInfo
+}
+
+func (vc *VidCache) Get(vid string) ([]Location, error) {
+	id, err := strconv.Atoi(vid)
+	if err != nil {
+		glog.V(1).Infof("Unknown volume id %s", vid)
+		return nil, err
+	}
+	if 0 < id && id <= len(vc.cache) {
+		if vc.cache[id-1].Locations == nil {
+			return nil, errors.New("Not Set")
+		}
+		if vc.cache[id-1].NextRefreshTime.Before(time.Now()) {
+			return nil, errors.New("Expired")
+		}
+		return vc.cache[id-1].Locations, nil
+	}
+	return nil, errors.New("Not Found")
+}
+func (vc *VidCache) Set(vid string, locations []Location, duration time.Duration) {
+	id, err := strconv.Atoi(vid)
+	if err != nil {
+		glog.V(1).Infof("Unknown volume id %s", vid)
+		return
+	}
+	if id > len(vc.cache) {
+		for i := id - len(vc.cache); i > 0; i-- {
+			vc.cache = append(vc.cache, VidInfo{})
+		}
+	}
+	if id > 0 {
+		vc.cache[id-1].Locations = locations
+		vc.cache[id-1].NextRefreshTime = time.Now().Add(duration)
+	}
+}