Add DiscriminatorValue method to IClassInstance

Fixes #134

+semver:feature

Author: hazzik

src/FluentNHibernate.Testing/ConventionsTests/ApplyingToModel/ClassConventionTests.cs

@@ -36,6 +36,14 @@ public void ShouldSetCacheProperty()
             VerifyModel(x => x.Cache.Usage.ShouldEqual("read-only"));
         }
 
+        [Test]
+        public void ShouldSetDiscriminatorValueProperty()
+        {
+            Convention(x => x.DiscriminatorValue("0"));
+
+            VerifyModel(x => x.DiscriminatorValue.ShouldEqual("0"));
+        }
+
         [Test]
         public void ShouldSetDynamicInsertProperty()
         {

src/FluentNHibernate/Conventions/Instances/ClassInstance.cs

@@ -38,6 +38,11 @@ public void Table(string tableName)
             mapping.Set(x => x.TableName, Layer.Conventions, tableName);
         }
 
+        public new void DiscriminatorValue(object value)
+        {
+            mapping.Set(x => x.DiscriminatorValue, Layer.Conventions, value);
+        }
+
         public new void DynamicInsert()
         {
             mapping.Set(x => x.DynamicInsert, Layer.Conventions, nextBool);

src/FluentNHibernate/Conventions/Instances/IClassInstance.cs

@@ -13,6 +13,7 @@ public interface IClassInstance : IClassInspector
         new ICacheInstance Cache { get; }
         new ISchemaActionInstance SchemaAction { get; }
         void Table(string tableName);
+        new void DiscriminatorValue(object value);
         new void DynamicInsert();
         new void DynamicUpdate();
         new void BatchSize(int size);
@@ -56,5 +57,6 @@ public interface IClassInstance : IClassInspector
         /// defining the filter to apply.
         /// </typeparam>
         void ApplyFilter<TFilter>() where TFilter : FilterDefinition, new();
+
     }
 }