Code review comment for lp:~nickpapior/siesta/4.1-fix-spin

I am ready to accept the changes on simplicity arguments (i.e., having a single, compatible way to build the DM in the Noncol and SOC cases).

I will merge this changes in my 4.1-spin-fix branch (which also contains other clarifications), and we will mark this branch for merging into OSSO when it is ready.