Avoid unnecessarily computing crc32c during downloads
Avoid unnecessarily computing crc32c during downloads

chriskuehl/gsutil-debian,dtjackson/gsutil,ttiurani/gsutil,fishjord/gsutil,dimfeld/gsutil,mattdr/gsutil,BrandonY/gsutil,GoogleCloudPlatform/gsutil,GoogleCloudPlatform/gsutil,craigcitro/gsutil