applyxfm4D results are incorrect
to reproduce:
datadir=/vols/Data/fsldev/dataSets/unit_tests/applyxfm4D/
fslroi $datadir/applyxfm4D_in twovol 0 2
flirt -in twovol -ref $datadir/applyxfm4D_ref -applyxfm -init $datadir/applyxfm4D_mat.mat -out flirted
applyxfm4D twovol $datadir/applyxfm4D_ref applied $datadir/applyxfm4D_mat.mat --singlematrix
mentioned by Paul: applyxfm4D seems to be clobbering the pixdims of the output image back to the pixdims of the input image, rather than those of the output