move to getter setter file

weed/util/bptree/getter_setter.go

@@ -0,0 +1,15 @@
+package bptree
+
+func (self *BpMap) getRoot() *BpNode {
+	return self.root
+}
+func (self *BpMap) setRoot(root *BpNode) {
+	self.root = root
+}
+
+func (self *BpTree) getRoot() *BpNode {
+	return self.root
+}
+func (self *BpTree) setRoot(root *BpNode) {
+	self.root = root
+}