roll back intent reply change

since earlier versions of NSB defaulted to a message intent of Send when
Return was called nor processing correlations messages based on message
intent is invalid.
-reverts
https://github.com/Particular/NServiceBus/commit/7707cfe27a26e39f4d0769ddb41a56e8228c2dcf
-re-opens https://github.com/Particular/NServiceBus/issues/2252
-add acceptance test to this doesnt happen again