Add warning to rsync command if running w/o compiled crcmod
Add warning to rsync command if running w/o compiled crcmod

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