MNT: Initial copy of Chris Rorden's gpu_test

gpu_test/ptest/masks/134.nii.gz

gpu_test/ptest/masks/135.nii.gz

gpu_test/ptest/masks/136.nii.gz

gpu_test/ptest/masks/137.nii.gz

gpu_test/ptest/masks/138.nii.gz

gpu_test/ptest/masks/139.nii.gz

gpu_test/ptest/masks/14.nii.gz

gpu_test/ptest/masks/140.nii.gz

gpu_test/ptest/masks/141.nii.gz

gpu_test/ptest/masks/142.nii.gz

gpu_test/ptest/masks/143.nii.gz

gpu_test/ptest/masks/144.nii.gz

gpu_test/ptest/masks/145.nii.gz

gpu_test/ptest/masks/146.nii.gz

gpu_test/ptest/masks/147.nii.gz

gpu_test/ptest/masks/148.nii.gz

gpu_test/ptest/masks/149.nii.gz

gpu_test/ptest/masks/15.nii.gz

gpu_test/ptest/masks/150.nii.gz

gpu_test/ptest/masks/151.nii.gz