bugfix of open_grid in the case spin==2 and wf_collect
Missing re-definition of isk inserted, which would cause the wrong filename to be used when nspin is 2 and wf_collect is used with new input/output subroutines
Missing re-definition of isk inserted, which would cause the wrong filename to be used when nspin is 2 and wf_collect is used with new input/output subroutines