Print stat messages to stderr to avoid logging filters
Print stat messages to stderr to avoid logging filters

Fixes https://github.com/GoogleCloudPlatform/gsutil/issues/288

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