NH-3884 - Default DateTime type can not be overridden

[fredericDelaporte]

NH-3884 (#844) - Default DateTime type can not be overridden

Here is a proposition for allowing overriding default clr type mapping to NHibernate type.

Such a method is quite low level, and for having a coherent session factory, it must be used before configuring and building the session factory. So I have put proper warnings in its comment.

Such a method could become handy if by doing NH-3919 as proposed here, we cause issues to some users.

[fredericDelaporte]

@hazzik, I think it would be better to merge this for v5.0 if ongoing #703 makes it too. This would give a way to revert the .Net DateTime default NHibernate type mapping semantic change for those who would need it.

[hazzik]

I don't want to merge this at this stage. There is a really high chance that these methods would be made obsolete in a possible future type refactoring. I think what we can do now is to make some of RegisterType methods public (anyway these methods do the same as your SetDefaultType does).

[fredericDelaporte]

The nearest is RegisterType(System.Type systemType, IType nhibernateType, IEnumerable<string> aliases) which takes an additional argument that will be unneeded for most users and also re-register the type alias (which should be unneeded for an override, but should not harm).

[fredericDelaporte]

I will likely split that in many PR.

[fredericDelaporte]

Rebased, the split in many PR and merge of the new PRs (#1483, #1484) having been done.