BF: fixed problem with NANs in odfdeconv

Add tests and fix for calculation of odf_deconv when NANs are present. 
This was identified by Dr. Jan Schreiber as reported in the mailing list. See discussion here: http://mail.scipy.org/pipermail/nipy-devel/2014-August/010419.html


You might also go with: 

    if np.any(np.isnan(odf_sh)):

I find that slightly clearer