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/assign_file_id.go

@@ -0,0 +1,48 @@
+package operation
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+	"strconv"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+type AssignResult struct {
+	Fid       string `json:"fid,omitempty"`
+	Url       string `json:"url,omitempty"`
+	PublicUrl string `json:"publicUrl,omitempty"`
+	Count     uint64 `json:"count,omitempty"`
+	Error     string `json:"error,omitempty"`
+}
+
+func Assign(server string, count uint64, replication string, collection string, ttl string) (*AssignResult, error) {
+	values := make(url.Values)
+	values.Add("count", strconv.FormatUint(count, 10))
+	if replication != "" {
+		values.Add("replication", replication)
+	}
+	if collection != "" {
+		values.Add("collection", collection)
+	}
+	if ttl != "" {
+		values.Add("ttl", ttl)
+	}
+	jsonBlob, err := util.Post("http://"+server+"/dir/assign", values)
+	glog.V(2).Info("assign result :", string(jsonBlob))
+	if err != nil {
+		return nil, err
+	}
+	var ret AssignResult
+	err = json.Unmarshal(jsonBlob, &ret)
+	if err != nil {
+		return nil, fmt.Errorf("/dir/assign result JSON unmarshal error:%v, json:%s", err, string(jsonBlob))
+	}
+	if ret.Count <= 0 {
+		return nil, errors.New(ret.Error)
+	}
+	return &ret, nil
+}