add new tests

svn path=/trunk/mcs/; revision=123496

mcs/class/System.Core/System.Core_test.dll.sources

@@ -4,7 +4,8 @@ System/TimeZoneInfo.TransitionTimeTest.cs
 System.Collections.Generic/HashSetTest.cs
 System.Linq/EnumerableTest.cs
 System.Linq/EnumerableMoreTest.cs
-System.Linq/EnumerableAsQueryableTest.cs
+System.Linq/EnumerableAsQueryableTest.cs
+System.Linq/LookupTest.cs
 System.Linq.Expressions/ExpressionTest.cs
 System.Linq.Expressions/ExpressionTest_Add.cs
 System.Linq.Expressions/ExpressionTest_AddChecked.cs