Update, changelog, setup.py, and submodules for 3.38 release.
Update, changelog, setup.py, and submodules for 3.38 release.

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