Fix xcrysden output
Fix the xcrysden output for non-orthogonal cells, due to a wrong transpose. Results was ok for fcc and bcc cells, as the lattice vector matrix is equal to its transpose. Octopus still verify rule 1 of DFT codes: everything works for Si.
Fix the xcrysden output for non-orthogonal cells
- I have checked that my code follows the Octopus coding standards
-  I have added tests for all the new features added in this request.