Solves issue 1512

This PR solves issue 1512 : https://github.com/Particular/NServiceBus/issues/1512

Is extends the 'TimeoutEntity_EndpointIdx' index with the Time column.

I have done a run-time test by using the NHibernate timeout persister in the pubsub sample and running NServiceBus.Host.exe -install to see if the table index was created correctly.