MNT: Initial copy of Chris Rorden's gpu_test

gpu_test/ptest/masks/170.nii.gz

gpu_test/ptest/masks/171.nii.gz

gpu_test/ptest/masks/172.nii.gz

gpu_test/ptest/masks/175.nii.gz

gpu_test/ptest/masks/176.nii.gz

gpu_test/ptest/masks/177.nii.gz

gpu_test/ptest/masks/178.nii.gz

gpu_test/ptest/masks/179.nii.gz

gpu_test/ptest/masks/18.nii.gz

gpu_test/ptest/masks/180.nii.gz

gpu_test/ptest/masks/181.nii.gz

gpu_test/ptest/masks/182.nii.gz

gpu_test/ptest/masks/183.nii.gz

gpu_test/ptest/masks/184.nii.gz

gpu_test/ptest/masks/185.nii.gz

gpu_test/ptest/masks/186.nii.gz

gpu_test/ptest/masks/187.nii.gz

gpu_test/ptest/masks/188.nii.gz

gpu_test/ptest/masks/189.nii.gz

gpu_test/ptest/masks/19.nii.gz