* Clean a bit the Triadiagonalization making sure it the inplace
function really works inplace ;), and that only the lower
triangular part of the matrix is referenced.
* Remove the Tridiagonalization member object of SelfAdjointEigenSolver
exploiting the in place capability of HouseholdeSequence.
* Update unit test to check SelfAdjointEigenSolver only consider
the lower triangular part.