reorder_img 'resample' argument sets interpolation resampling

Also:
* niimg variable names should end with _img in test_resampling.py
* fix PEP8 and typo axis -> axes
* add value of interpolation in resample_img error message
Merge pull request #270 from lesteve/reorder-with-resample-args

Add resampling arguments to nilearn.image.resampling.reorder_img