Put nvidia-current (and later, fglrx package) into ltsp image.
These are tricky because they break other drivers,
and fglrx even conflicts with nvidia-current.
We try to use the upstream packages, and play the necessary
alternatives/ldconfig-tricks elsewhere.
Simplify the fglrx/nvidia configuration codes a bit
(and do not even pretend to handle the (!= i386) case
that we are not testing anyway.