MNT: Initial copy of Chris Rorden's gpu_test

gpu_test/ptest/masks/74.nii.gz

gpu_test/ptest/masks/75.nii.gz

gpu_test/ptest/masks/76.nii.gz

gpu_test/ptest/masks/77.nii.gz

gpu_test/ptest/masks/78.nii.gz

gpu_test/ptest/masks/79.nii.gz

gpu_test/ptest/masks/8.nii.gz

gpu_test/ptest/masks/80.nii.gz

gpu_test/ptest/masks/81.nii.gz

gpu_test/ptest/masks/82.nii.gz

gpu_test/ptest/masks/83.nii.gz

gpu_test/ptest/masks/84.nii.gz

gpu_test/ptest/masks/85.nii.gz

gpu_test/ptest/masks/86.nii.gz

gpu_test/ptest/masks/87.nii.gz

gpu_test/ptest/masks/88.nii.gz

gpu_test/ptest/masks/89.nii.gz

gpu_test/ptest/masks/9.nii.gz

gpu_test/ptest/masks/90.nii.gz

gpu_test/ptest/masks/91.nii.gz