Bug#789090: nvidia-cuda-toolkit: missing libncurses5 build dependency

[Sven Joachim]

Source: nvidia-cuda-toolkit
Version: 6.0.37-5

The nvidia-cuda-gdb package depends on libncurses5 (>= 5.5-5~) which is
apparently deduced by dpkg-shlibdeps.  There should be a build
dependency on libncurses5 to ensure that this keeps working.

While libncurses5 us currently in the essential packages' closure set,
that is subject to change.