Obsolete FluentNHibernate.Data.Entity

[hazzik]

The FluentNHibernate.Data.Entity class is problematic because of the following:

• It does not consider transient entities (see Modify Entity.Equals to Return False When Both IDs are Zero #376)
• It does not uphold the requirement to have a stable GetHashCode() during the lifetime of the entity
• It probably does have a bug working with proxies as it checks for a concrete type.

Instead of using FluentNHibernate.Data.Entity please implement your own.

Closes #376

[hazzik]

The good implementation for base class for entity could be found here: https://stackoverflow.com/a/5857854/259946 and here https://ayende.com/blog/2500/generic-entity-equality