Move UID handling from Base

Also clean up some of the value creation code.

graph/iterator/and_iterator.go

@@ -26,6 +26,7 @@ import (
 // be Next()ed if next is called.
 type And struct {
 	Base
+	uid               uint64
 	tags              graph.Tagger
 	internalIterators []graph.Iterator
 	itCount           int
@@ -35,13 +36,18 @@ type And struct {
 
 // Creates a new And iterator.
 func NewAnd() *And {
-	var and And
+	and := And{
+		uid:               NextUID(),
+		internalIterators: make([]graph.Iterator, 0, 20),
+	}
 	BaseInit(&and.Base)
-	and.internalIterators = make([]graph.Iterator, 0, 20)
-	and.checkList = nil
 	return &and
 }
 
+func (it *And) UID() uint64 {
+	return it.uid
+}
+
 // Reset all internal iterators
 func (it *And) Reset() {
 	it.primaryIt.Reset()