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/storage/needle_byte_cache.go

@@ -0,0 +1,75 @@
+package storage
+
+import (
+	"fmt"
+	"os"
+	"sync/atomic"
+
+	"github.com/hashicorp/golang-lru"
+
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+var (
+	bytesCache *lru.Cache
+	bytesPool  *util.BytesPool
+)
+
+/*
+There are one level of caching, and one level of pooling.
+
+In pooling, all []byte are fetched and returned to the pool bytesPool.
+
+In caching, the string~[]byte mapping is cached
+*/
+func init() {
+	bytesPool = util.NewBytesPool()
+	bytesCache, _ = lru.NewWithEvict(512, func(key interface{}, value interface{}) {
+		value.(*Block).decreaseReference()
+	})
+}
+
+type Block struct {
+	Bytes    []byte
+	refCount int32
+}
+
+func (block *Block) decreaseReference() {
+	if atomic.AddInt32(&block.refCount, -1) == 0 {
+		bytesPool.Put(block.Bytes)
+	}
+}
+func (block *Block) increaseReference() {
+	atomic.AddInt32(&block.refCount, 1)
+}
+
+// get bytes from the LRU cache of []byte first, then from the bytes pool
+// when []byte in LRU cache is evicted, it will be put back to the bytes pool
+func getBytesForFileBlock(r *os.File, offset int64, readSize int) (dataSlice []byte, block *Block, err error) {
+	// check cache, return if found
+	cacheKey := fmt.Sprintf("%d:%d:%d", r.Fd(), offset>>3, readSize)
+	if obj, found := bytesCache.Get(cacheKey); found {
+		block = obj.(*Block)
+		block.increaseReference()
+		dataSlice = block.Bytes[0:readSize]
+		return dataSlice, block, nil
+	}
+
+	// get the []byte from pool
+	b := bytesPool.Get(readSize)
+	// refCount = 2, one by the bytesCache, one by the actual needle object
+	block = &Block{Bytes: b, refCount: 2}
+	dataSlice = block.Bytes[0:readSize]
+	_, err = r.ReadAt(dataSlice, offset)
+	bytesCache.Add(cacheKey, block)
+	return dataSlice, block, err
+}
+
+func (n *Needle) ReleaseMemory() {
+	if n.rawBlock != nil {
+		n.rawBlock.decreaseReference()
+	}
+}
+func ReleaseBytes(b []byte) {
+	bytesPool.Put(b)
+}