nilearn.image.resample_img given 4D affine but not target_shape behaviour to be changed

Addressing issue https://github.com/nilearn/nilearn/issues/174

Proposed is a test to show that resample_img doesn't do what one would expect it to do when a 4D affine is given and no target shape specified. It keeps the old shape, leading to potentially a total loss of the relevant data from field of view.

Remedy to follow