add LOAD_NONE

[iritkatriel]

Old:

iritkatriel@Irits-MBP cpython-1 % ./python.exe -c "import dis; dis.dis('x=None')"
  1           0 LOAD_CONST               0 (None)
              2 STORE_NAME               0 (x)
              4 LOAD_CONST               0 (None)
              6 RETURN_VALUE
iritkatriel@Irits-MBP cpython-1 % repeat 5 ./python.exe -m timeit "x = None"     
20000000 loops, best of 5: 15.1 nsec per loop
20000000 loops, best of 5: 15.1 nsec per loop
20000000 loops, best of 5: 15.1 nsec per loop
20000000 loops, best of 5: 15.3 nsec per loop
20000000 loops, best of 5: 15.1 nsec per loop

New:

iritkatriel@Irits-MBP cpython % ./python.exe -c "import dis; dis.dis('x=None')"
  1           0 LOAD_NONE
              2 STORE_NAME               0 (x)
              4 LOAD_NONE
              6 RETURN_VALUE
iritkatriel@Irits-MBP cpython % repeat 5 ./python.exe -m timeit "x = None"     
20000000 loops, best of 5: 14.9 nsec per loop
20000000 loops, best of 5: 14.9 nsec per loop
20000000 loops, best of 5: 14.8 nsec per loop
20000000 loops, best of 5: 14.8 nsec per loop
20000000 loops, best of 5: 14.8 nsec per loop