fmatrixtest fails to compile with the current master of Vc

The reason is that Vc does not yield plain references anymore when accessing entries of simd vectors and masks, but proxy objects. These proxy objects are non-copyable and non-movable. This means that our abstraction for accessing entries of such vectors and masks, the function lane(), cannot return these proxies.

There is an updated simd interface that I (@joe) am working on in !193 (merged). That circumvents this issue by using it's own proxy class.

I currently intend to fix this by replacing the old interface by the one from !193 (merged), eventually.