MNT: Initial copy of Chris Rorden's gpu_test

gpu_test/ptest/masks/152.nii.gz

gpu_test/ptest/masks/153.nii.gz

gpu_test/ptest/masks/154.nii.gz

gpu_test/ptest/masks/155.nii.gz

gpu_test/ptest/masks/156.nii.gz

gpu_test/ptest/masks/157.nii.gz

gpu_test/ptest/masks/158.nii.gz

gpu_test/ptest/masks/159.nii.gz

gpu_test/ptest/masks/16.nii.gz

gpu_test/ptest/masks/160.nii.gz

gpu_test/ptest/masks/161.nii.gz

gpu_test/ptest/masks/162.nii.gz

gpu_test/ptest/masks/163.nii.gz

gpu_test/ptest/masks/164.nii.gz

gpu_test/ptest/masks/165.nii.gz

gpu_test/ptest/masks/166.nii.gz

gpu_test/ptest/masks/167.nii.gz

gpu_test/ptest/masks/168.nii.gz

gpu_test/ptest/masks/169.nii.gz

gpu_test/ptest/masks/17.nii.gz