Enable non-interactive use

[mih]

Demo from Python

>>> e=FSLtoNIDMExporter(out_dirname='/tmp/nidmfslout', zipped=False, feat_dir='sub-01/2ndlvl.gfeat/cope1.feat', groups=['control', 1])
/tmp/nidmfslout.nidm already exists, overwrite? (y/N) 

I think it would be better to test for this case in the command line argument handling in such an interactive way. For the Python API it would be better to have it raise an exception (that can be acted one), and add a force option to enable silent overwriting.

[cmaumet]

Thanks for this suggestion! Sounds good to me. I'll implement it.