Improved debugging output

Use ToString of the expression as message, this allows usage of
PartialEvaluationExceptionExpression ToString output

Author: janv8000

src/NHibernate/Linq/Visitors/HqlGeneratorExpressionTreeVisitor.cs

@@ -139,7 +139,7 @@ protected HqlTreeNode VisitExpression(Expression expression)
 							//    return VisitNhNew((NhNewExpression)expression);
 					}
 
-					throw new NotSupportedException(expression.GetType().Name);
+					throw new NotSupportedException(expression.ToString());
 			}
 		}