The Raven UoW now call ReleaseSession on the session factory to make sure
we release and dispose the session for each message. Remove the
IDisposable from the session factory to avoid confusion. Closes #965
Merge branch 'develop' of git://github.com/NServiceBus/NServiceBus into develop

Conflicts:
	src/NServiceBus.Core/Persistence/Raven/RavenSessionFactory.cs