Bug#770588: Bug#769072, #769191, #770588: nvidia-opencl-icd breaking non-nvidia systems

[Rebecca N. Palmer]

(Should we merge these bugs?  Also, #767803 looks like another instance 
of this, though it doesn't have the apt log to confirm it yet)

> * nvidia-kernel-dkms: Switch to Recommends: nvidia-driver | libcuda1
>   to break the chain libcuda1 -> nvidia-kernel-dkms -> nvidia-driver.
...or drop this Recommends: entirely (IIRC circular Depends/Recommends 
are discouraged because they confuse apt's autoremover, though I can't 
find where I saw that).

Cutting the chain here (tested with "apt-get install nvidia-libopencl1 
nvidia-driver-", the - after a package means "remove/don't install") 
does still allow much of nvidia-* (including nvidia-kernel-dkms and 
glx-alternative-nvidia) to be installed, but that appears to be harmless 
without libgl1-nvidia-glx (at least on my Intel IvyBridge M GT2, both 
graphics and OpenCL continue to work after rebooting).

Given that the error on loading nvidia-opencl-icd in a non-Nvidia system is

modprobe: ERROR: could not insert 'nvidia_current': No such device

it is plausible that nvidia-opencl-icd uses the nvidia kernel module 
(i.e. nvidia-kernel-dkms | nvidia-kernel-<version>) and as such _should_ 
pull it in (whether or not it also needs libcuda1), while #768185 
suggests that nvidia-opencl-icd works without the graphics side (can 
someone check that?), making this the more correct place to cut the chain.