fix build

Author: bahusoid

src/NHibernate.Test/Linq/ConstantTest.cs

@@ -4,6 +4,7 @@
 using NHibernate.Criterion;
 using NHibernate.DomainModel.Northwind.Entities;
 using NHibernate.Engine.Query;
+using NHibernate.Linq;
 using NHibernate.Linq.Visitors;
 using NHibernate.Util;
 using NUnit.Framework;