`::StdPowerMeasure{MU,1}` pattern

[cscherrer]

In product_transport.jl, I see a lot of methods with arguments like

 μ::StdPowerMeasure{MU,1}

This complicates dispatch, and I don't see why it's necessary. @oschulz Why do we need to treat vector specially? I'd think we could just reshape as needed and it could be simpler, but maybe I'm missing something.

[oschulz]

Let me take another look - I think there was a reason for it, but I have to remind myself :-)