Commit dabdc917 fixed the tgt vector and matrix implementation to follow strict aliasing rules but also changed the semantics of the sub-vector/sub-matrix getters, which previously returned references but after returned copies.
While this did not break CAMPVis code, since nobody relied on it, the original reference semantics were much more intuitive. This commit brings them back but in a valid C++ way not breaking strict aliasing rules.

closes #545