Implement Decimal.Truncate

Author: hazzik

src/NHibernate.Test/NHSpecificTest/GH0831/FixtureByCode.cs

@@ -135,6 +135,18 @@ public void CanHandleFloor()
 				CanSelect(e => decimal.Floor(e.EntityValue));
 			});
 		}
+	
+		[Test]
+		public void CanHandleTruncate()
+		{
+			AssumeFunctionSupported("truncate");
+
+			Assert.Multiple(() =>
+			{
+				CanFilter(e => decimal.Truncate(e.EntityValue) > 1.0m);
+				CanSelect(e => decimal.Truncate(e.EntityValue));
+			});
+		}
 
 		[Test]
 		public void CanHandleMultiply()

src/NHibernate/Linq/Functions/MathGenerator.cs

@@ -55,6 +55,7 @@ public MathGenerator()
 
 				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(decimal))),
 				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(double))),
+				ReflectHelper.GetMethodDefinition(() => decimal.Truncate(default(decimal))),
 
 				ReflectHelper.GetMethodDefinition(() => Math.Pow(default(double), default(double))),
 			};