Fix bug with features of different type than float64
Fix bug with features of different type than float64

The created image for visualizing patches should maintain
the dtype of the features array otherwise the Cython code
will fail.

patricksnape/menpo,patricksnape/menpo,yuxiang-zhou/menpo,yuxiang-zhou/menpo,grigorisg9gr/menpo,grigorisg9gr/menpo,menpo/menpo,grigorisg9gr/menpo,menpo/menpo,menpo/menpo,patricksnape/menpo,yuxiang-zhou/menpo