dev-util/nvidia-cuda-toolkit: add version 6.5.19

NVIDIA has release a CUDA 6.5 Production Release with Support for GeForce GTX9xx GPUs. This version does not replace version 6.5.14, which is still the first choice when downloading CUDA from the NVIDIA website [1].
Therefore it would be useful if both versions are offered.

[1] https://developer.nvidia.com/cuda-downloads