This is a preparatory commit for using isort for sorting all of our
imports, merging changes to files where we can easily review the
changes as something we're happy with.
These are also files with relatively little active development, which
means we don't expect much merge conflict risk from these changes.
This avoids a spurious permission error inside the Postgres
`resolve_symlinks` function if we don’t have access to the current
working directory (e.g. we’re running with cwd /root inside `su
zulip`).
While we’re here, add a defensive `--` argument.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>