BUG: stopped vasp calculator from witing a KPOINTS file when KSPACING is specified.
Previous behaviour continued to write a default Gamma point KPOINTS file, even when KSPACING was defined. This resulted in VASP over-riding the KSPACING COMMAND. The fix is to set kpts to () when KSPACING is defined, then to disable writing the KPOINTS file if len(kpts)=0.