Make gsutil output command synopsis when run with wrong number of args
Fix defacl ch on private-acl bucket
Fix tab completion failure when argcomplete not available
Fix bug where rm command didn't support preconditions header
Add tab completion support for remaining commands.
Implement no-op completer for use in notification command.
Test file completer in subcommand completion test.
Fix tab completion when request is not a valid URL but can complete to a valid URL.
Fix unit test failures with argcomplete present.
Add doc to rm command about restoring accidentally deleted data
Make gsutil commands output better help for invalid sub-arguments
Improve missing object detection after upload
Fix grammar of 'requires at least' warning
Fix XML failure in test_rm_failing_precondition
Add background comment to MockCloudApi
Add bucket-only completer for commands that only work on buckets.
Add timeout for tab completions involving remote requests.
Add simple caching for tab completion results.
Reduce num_retries for anonymous tests.

This reduces parallel test runtime substantially because tests involving anonymous auth are no longer a long tail.
Prefix matching for tab completion cache.