Fix stateless batcher

[fredericDelaporte]

Fix #2750.

[fredericDelaporte]

This is more consistent with the stateless semantic of a stateless session, and also with:

nhibernate-core/src/NHibernate/Impl/SessionFactoryImpl.cs

Line 1605 in 07ecb9f

public FlushMode InitialSessionFlushMode => FlushMode.Always;

(That is in the stateless session builder.)

[hazzik]

Need to restrict tests to the providers that support distributed transactions.

[fredericDelaporte]

I have amended the "more test" commit and rebased.

[hazzik]

StatelessSession has ManagedFlush method which is not exposed through interface. Maybe we should expose it instead?

[fredericDelaporte]

I choosed FlushBatcher rather than just Flush because in principle the stateless session should never need a Flush, since it is stateless. So I want to stress what this flush is for: flushing the batcher that can be enabled with the stateless session, and which may retain some operations not yet sent to the database.

[hazzik]

Just wanted to clarify that I'm not talking about the general Flush method, but about ManagedFlush.

[fredericDelaporte]

In the case of the stateless session, that is the same.

But anyway, what does it mean, ManagedFlush? I do not make any sense of it. FlushBatcher is explicit about its purpose, while that is not the case of ManagedFlush in my opinion.

nhibernate-core/src/NHibernate/Impl/StatelessSessionImpl.cs

Lines 385 to 396 in 2bd3c16

	public override void Flush()
	{
	ManagedFlush(); // NH Different behavior since ADOContext.Context is not implemented
	}
	public void ManagedFlush()
	{
	using (BeginProcess())
	{
	Batcher.ExecuteBatch();
	}
	}