Add option to run arguments in pairs instead of cartesian product

[samuelstjean]

smart_dispatch.py -q qwork@mp2 -t 15:00:00 script.py [infile1.nii.gz infile2.nii.gz ] interface.nii.gz [outfile1.trk outfile2.trk ] --tq

So, according to the example this will run 4 lines, with the combinations of infile(1,2) with outfile(1,2).

Would be useful to have an option to take each pair instead, that is 2 commands with (infile1,outfile1) and (infile2,outfile2), where the combinations of infile1/outifle2 and infile2/outfile1 makes no sense for some usecase, and actually clobber each other.