Previously, the repository owner+name component of the URL was ignored
and only the pull request number was read. Now, the URL dictates which
base repository will be used.
This stubs stderr separately from stdout in command tests (before those
streams were combined) and improves test assertions around output.
Additionally, no longer use the `cmd.Print*()` family of Cobra functions
because their name sounds like the text will go to stdout, but they
write to stderr instead. Use the more explicit `cmd.ErrOrStderr()` as
output destination instead.
