corrects saving of bootstraps
corrects saving of bootstraps

the 5d models matrix contains the individual bootstraps data, but is too
big to save to one giant 5d nifti, so instead we save each stimulus
class as a separate nifti, so the different parts of the volume
correspond to the different bootstraps.

billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences