* gc: make it safer by only activating by use of certain flags
Previous plain `gc` is now not supported. The same behavior can be trigger by
`gc -w` or `gc --workspace`. When `--all-{tags, commits, branches}` are
specified, it will work as if `-w` is also specified (same as before).
* tests: adjust gc to use workspace on test_repro
- `tmp_dir` descends from Path
- convenient template methods to generate files and dirs, add them to
dvc and git and commit to git
- independent of old basic_env structures
- can go in any order
- modular: start with empty `tmp_dir`, initialize git with `scm`, dvc
repo with `dvc` add "repo template" with `repo_template`, ...
* dvc: fix branch suffixes in status/push/pull
* gc: add --all-commits flag
* gc: fix gc warning
Say that we always leave things used in the working tree