Fix firebird tests

Author: maca88

src/NHibernate/Dialect/FirebirdDialect.cs

@@ -417,7 +417,7 @@ private void OverrideStandardHQLFunctions()
 			RegisterFunction("nullif", new StandardSafeSQLFunction("nullif", 2));
 			RegisterFunction("lower", new StandardSafeSQLFunction("lower", NHibernateUtil.String, 1));
 			RegisterFunction("upper", new StandardSafeSQLFunction("upper", NHibernateUtil.String, 1));
-			RegisterFunction("mod", new StandardSafeSQLFunction("mod", NHibernateUtil.Double, 2));
+			RegisterFunction("mod", new StandardSafeSQLFunction("mod", NHibernateUtil.Int32, 2));
 			RegisterFunction("str", new SQLFunctionTemplate(NHibernateUtil.String, "cast(?1 as VARCHAR(255))"));
 			RegisterFunction("strguid", new StandardSQLFunction("uuid_to_char", NHibernateUtil.String));
 			RegisterFunction("sysdate", new CastedFunction("today", NHibernateUtil.Date));