Reading DM file with different spin order

This is a bug / feature request:

A requirement for reading the DM file is that it must have the same the spin order (non-polarized, spin-polarized, non-collinear or spin orbit) as the current calculation. However, some times it is interesting to use a DM with lower spin order in a higher spin order calculation. For example, using a non-polarized DM to initialize a spin-polarized calculation, or a spin-polarized DM to initialize a spin-orbit calculation. This is implemented in A.Postnikov utility DMtune (http://www.home.uni-osnabrueck.de/apostnik/Software/DMtune.tar.gz) and it could be added to the SIESTA initialization routines.

The heuristics could be: if a DM with lower spin order but correct number of orbitals is found, it is expanded to the desired spin order. If the DM file is non-polarized, DM.InitSpin could be used to initialize the spin as desired. Additionally, an option could be added to rotate the magnetization for non-collinear and spin-orbit calculations. This option would facilitate the calculation of, for example, magnetic anisotropy energies.