Add resampling arguments to nilearn.image.resampling.reorder_img

When using `resample=True` in `nilearn.image.resampling.reorder_img` it could be useful to specify additional resampling arguments. The use case that @mrahim had:

* he wants to plot segmentation images with a discrete set of values (one value per region).
* Using `plot_img` yields an error because his affine can not be made diagonal by reordering the axes. 
* Trying to use reorder_img explicitly with resample=True resamples the image with some interpolation which mangles the region you are trying to see: 
![resampled_segmentation](https://cloud.githubusercontent.com/assets/1680079/4808303/089f7658-5e9f-11e4-9ab5-66ef1cf64088.png). This is the picture you would expect:
![resampled_segmentation_nearest](https://cloud.githubusercontent.com/assets/1680079/4808331/51b47032-5e9f-11e4-89ec-8cf91d87d299.png)