NH-3496 - fix sequence drop if sequence does not exist.
NH-2963 - Exception when map an IList(Of T) by Code in VB.NET
fixup! NH-2963 - Exception when map an IList(Of T) by Code in VB.NET
NH-3505 - Check transience via unsaved id to eliminate need for hydrating entities to get version.  Fixes lazy many-to-ones on versioned classes with stateless session updates.