Fix constant value in function cached in LINQ query

 * Fixes #1330 (NH-3673)
 * Allows a workaround for #1363 (NH-2500)

Author: fredericDelaporte

src/NHibernate.Test/Async/Linq/ConstantTest.cs

@@ -175,11 +175,16 @@ public int GetItemValue(Product p)
 			{
 				return _value;
 			}
+
+			// Workaround for object instance caching. Without this, ObjectConstants test fails.
+			public override string ToString()
+			{
+				return base.ToString() + _value;
+			}
 		}
 
 		// Adapted from NH-2500 first test case by Andrey Titov (file NHTest3.zip)
 		[Test]
-		[Ignore("Not fixed yet")]
 		public async Task ObjectConstantsAsync()
 		{
 			var builder = new InfoBuilder(1);
@@ -200,7 +205,6 @@ private int TestFunc(Product item, int closureValue)
 
 		// Adapted from NH-3673
 		[Test]
-		[Ignore("Not fixed yet")]
 		public async Task ConstantsInFuncCallAsync()
 		{
 			var closureVariable = 1;

src/NHibernate.Test/Linq/ConstantTest.cs

@@ -163,11 +163,16 @@ public int GetItemValue(Product p)
 			{
 				return _value;
 			}
+
+			// Workaround for object instance caching. Without this, ObjectConstants test fails.
+			public override string ToString()
+			{
+				return base.ToString() + _value;
+			}
 		}
 
 		// Adapted from NH-2500 first test case by Andrey Titov (file NHTest3.zip)
 		[Test]
-		[Ignore("Not fixed yet")]
 		public void ObjectConstants()
 		{
 			var builder = new InfoBuilder(1);
@@ -188,7 +193,6 @@ private int TestFunc(Product item, int closureValue)
 
 		// Adapted from NH-3673
 		[Test]
-		[Ignore("Not fixed yet")]
 		public void ConstantsInFuncCall()
 		{
 			var closureVariable = 1;

src/NHibernate/Linq/Visitors/ExpressionKeyVisitor.cs

@@ -163,20 +163,21 @@ protected override Expression VisitMethodCall(MethodCallExpression expression)
 		{
 			var old = insideSelectClause;
 
-			switch (expression.Method.Name)
-			{
-				case "First":
-				case "FirstOrDefault":
-				case "Single":
-				case "SingleOrDefault":
-				case "Select":
-				case "GroupBy":
-					insideSelectClause = true;
-					break;
-				default:
-					insideSelectClause = false;
-					break;
-			}
+			if (expression.Method.DeclaringType?.Namespace == "System.Linq")
+				switch (expression.Method.Name)
+				{
+					case "First":
+					case "FirstOrDefault":
+					case "Single":
+					case "SingleOrDefault":
+					case "Select":
+					case "GroupBy":
+						insideSelectClause = true;
+						break;
+					default:
+						insideSelectClause = false;
+						break;
+				}
 
 			Visit(expression.Object);
 			_string.Append('.');