MNT: Initial copy of Chris Rorden's gpu_test

gpu_test/ptest/masks/116.nii.gz

gpu_test/ptest/masks/117.nii.gz

gpu_test/ptest/masks/118.nii.gz

gpu_test/ptest/masks/119.nii.gz

gpu_test/ptest/masks/12.nii.gz

gpu_test/ptest/masks/120.nii.gz

gpu_test/ptest/masks/121.nii.gz

gpu_test/ptest/masks/122.nii.gz

gpu_test/ptest/masks/123.nii.gz

gpu_test/ptest/masks/124.nii.gz

gpu_test/ptest/masks/125.nii.gz

gpu_test/ptest/masks/126.nii.gz

gpu_test/ptest/masks/127.nii.gz

gpu_test/ptest/masks/128.nii.gz

gpu_test/ptest/masks/129.nii.gz

gpu_test/ptest/masks/13.nii.gz

gpu_test/ptest/masks/130.nii.gz

gpu_test/ptest/masks/131.nii.gz

gpu_test/ptest/masks/132.nii.gz

gpu_test/ptest/masks/133.nii.gz