query: add Statement method to return generated statement. (#1113)

Closes #1108

session.go

@@ -681,10 +681,15 @@ func (q *Query) defaultsFromSession() {
 	q.rt = s.cfg.RetryPolicy
 	q.serialCons = s.cfg.SerialConsistency
 	q.defaultTimestamp = s.cfg.DefaultTimestamp
-  q.idempotent = s.cfg.DefaultIdempotence
+	q.idempotent = s.cfg.DefaultIdempotence
 	s.mu.RUnlock()
 }
 
+// Statement returns the statement that was used to generate this query.
+func (q Query) Statement() string {
+	return q.stmt
+}
+
 // String implements the stringer interface.
 func (q Query) String() string {
 	return fmt.Sprintf("[query statement=%q values=%+v consistency=%s]", q.stmt, q.values, q.cons)