fixing nhibernate.test and adding knownbug attribute

Author: RogerKratz

src/NHibernate.Test/NHSpecificTest/NH3570/BiFixture.cs

@@ -10,6 +10,7 @@ public class BiFixture : BugTestCase
 		private Guid id;
 
 		[Test]
+		[KnownBug("NH-3570")]
 		public void ShouldNotSaveRemoveChild()
 		{
 			var parent = new BiParent();

src/NHibernate.Test/NHSpecificTest/NH3570/UniFixture.cs

@@ -10,6 +10,7 @@ public class UniFixture : BugTestCase
 		private Guid id;
 
 		[Test]
+		[KnownBug("NH-3570")]
 		public void ShouldNotSaveRemoveChild()
 		{
 			var parent = new UniParent();