Add support UNION QueryOver NHibernate

[fernandocode]

I need to make a UNION between two queries, and I always decided to make a union in memory (Concat) and now I have a situation where I page the result and with UNION, I would only be able to do this if I brought everything to memory but this is infeasible.

I would like to know the plans for support and this, or if you have any reasonable options for UNION currently.

This is being a big problem in development, and it no longer makes sense to use NHibernate for my queries.

I saw that there are tests ready for when this is implemented, is there planning? https://github.com/nhibernate/nhibernate-core/blob/master/src/NHibernate.Test/Linq/LinqQuerySamples.cs#L1149-L1235