Enable WCF hosting in unobtrusive mode, fixes #889

Conflicts:
	src/NServiceBus.Core/Hosting/GenericHost.cs
	src/NServiceBus.Core/Hosting/Wcf/WcfManager.cs
Merge branch '3.3.4'
Merge branch '3.3.4' into develop

Conflicts:
	src/hosting/NServiceBus.Hosting/GenericHost.cs
	src/hosting/NServiceBus.Hosting/Wcf/WcfManager.cs
Exceptions on Scope.Complete causes message failures to not increment, fixes #891