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/sequence/memory_sequencer.go

@@ -0,0 +1,36 @@
+package sequence
+
+import (
+	"sync"
+)
+
+// just for testing
+type MemorySequencer struct {
+	counter      uint64
+	sequenceLock sync.Mutex
+}
+
+func NewMemorySequencer() (m *MemorySequencer) {
+	m = &MemorySequencer{counter: 1}
+	return
+}
+
+func (m *MemorySequencer) NextFileId(count uint64) (uint64, uint64) {
+	m.sequenceLock.Lock()
+	defer m.sequenceLock.Unlock()
+	ret := m.counter
+	m.counter += uint64(count)
+	return ret, count
+}
+
+func (m *MemorySequencer) SetMax(seenValue uint64) {
+	m.sequenceLock.Lock()
+	defer m.sequenceLock.Unlock()
+	if m.counter <= seenValue {
+		m.counter = seenValue + 1
+	}
+}
+
+func (m *MemorySequencer) Peek() uint64 {
+	return m.counter
+}

weed/sequence/sequence.go

@@ -0,0 +1,7 @@
+package sequence
+
+type Sequencer interface {
+	NextFileId(count uint64) (uint64, uint64)
+	SetMax(uint64)
+	Peek() uint64
+}