Created by: jerrywgz
Fix https://github.com/PaddlePaddle/PaddleDetection/issues/84
- Fix im_info when max_size!=0, and have checked the mAP for faster_rcnn_r50_1x, mask_rcnn_r50_1x, faster_rcnn_r50_vd_1x
- Round numbers may cause inconsistency in (resized_w/im_w, resized_h/im_h, im_scale) and resize of PIL will introduce minor error. As a result, set use_cv2=True to be required when max_size!=0.