discard the crop image when skip rotation

[jiandan42]

It seems that the original image instead of the cropped image will be fed into the blob if you skip the rotation process(set rotation_interval=1). In src/caffe/data_transformer.cpp, the cv_img is cropped and stored in cv_cropped_img. Then in the rotation process, the cv_cropped_img is rotated and stored back in cv_img. At last, the cv_img is fed into the blob. So if you skip the rotation process, the cv_img is directly fed into the blob and the croped image is discarded.