Change notation in KS_Solvers
Notation inside KS_Solvers has been slighyly changed to distinguish between function pointers (e.g. h_psi_ptr, s_psi_ptr) and "real" PW subroutines (e.g. h_psi, h_psi_gpu, s_psi, s_psi_gpu).
rotate_xpsi now uses function pointers instead of PW subroutines.
Edited by Ivan Carnimeo