Add support Cache.never new NHibernate feature

[gokhanabatay]

Hi, For perfromance needs NHibernate now supports to exclude desired entities from second level cache features. https://github.com/nhibernate/nhibernate-core/pull/2744

Could you add support Cache.Never() for FluentNHibernate mapping.

public class EntUserPolicyDefMap : ClassMap<EntUserPolicyDef>
{
        public EntUserPolicyDefMap()
        {
               Cache.Never();
        }
}

Does Cache.CustomUsage("never") is a option to set cache strategy.

[gokhanabatay]

Its working with Cache.CustomUsage("never") in fluent nhibernate mapping file