Fix PostgreSQL bitwise xor registration

Fixes nhibernate#1673

Author: fredericDelaporte

src/NHibernate/Dialect/PostgreSQLDialect.cs

@@ -84,6 +84,7 @@ public PostgreSQLDialect()
 			RegisterFunction("atan2", new StandardSQLFunction("atan2", NHibernateUtil.Double));
 
 			RegisterFunction("power", new StandardSQLFunction("power", NHibernateUtil.Double));
+			RegisterFunction("bxor", new BitwiseNativeOperation("#"));
 
 			RegisterFunction("floor", new StandardSQLFunction("floor"));
 			RegisterFunction("ceiling", new StandardSQLFunction("ceiling"));