NV-CONTROL: Returning None if Coolbit 4 is not set
NV-CONTROL: Returning None if Coolbit 4 is not set

Previously it was not possible to know if the manual control was simply
disabled or if the coolbit 4 was not set at all. Now the function
returns None if the coolbit is not set at all or a boolean if is set.

python-xlib/python-xlib,python-xlib/python-xlib